Report a bug
If you spot a problem with this page, click here to create a Bugzilla issue.
Improve this page
Quickly fork, edit online, and submit a pull request for this page.
Requires a signed-in GitHub account. This works well for small changes.
If you'd like to make larger changes you may want to consider using
a local clone.
std.experimental.checkedint
This module defines facilities for efficient checking of integral operations
against overflow, casting with loss of precision, unexpected change of sign,
etc. The checking (and possibly correction) can be done at operation level, for
example opChecked!"+"(x, y, overflow) adds two integrals x and
y and sets overflow to true if an overflow occurred. The flag overflow
(a bool passed by reference) is not touched if the operation succeeded, so the
same flag can be reused for a sequence of operations and tested at the end.
Issuing individual checked operations is flexible and efficient but often
tedious. The Checked facility offers encapsulated integral wrappers that
do all checking internally and have configurable behavior upon erroneous
results. For example, Checked!int is a type that behaves like int but aborts
execution immediately whenever involved in an operation that produces the
arithmetically wrong result. The accompanying convenience function checked uses type deduction to convert a value x of integral type T to
Checked!T by means of checked(x). For example:
These policies may be used alone, e.g. Checked!(uint, WithNaN) defines a
uint-like type that reaches a stable NaN state for all erroneous operations.
They may also be "stacked" on top of each other, owing to the property that a
checked integral emulates an actual integral, which means another checked
integral can be built on top of it. Some combinations of interest include:
The hook's members are looked up statically in a Design by Introspection manner
and are all optional. The table below illustrates the members that a hook type
may define and their influence over the behavior of the Checked type using it.
In the table, hook is an alias for Hook if the type Hook does not
introduce any state, or an object of type Hook otherwise.
void main() { import std.experimental.checkedint, std.stdio; writeln((checked(5) + 7).get); // 12 writeln((checked(10) * 1000 * 1000 * 1000).get); // Overflow }Similarly, checked(-1) > uint(0) aborts execution (even though the built-in comparison int(-1) > uint(0) is surprisingly true due to language's conversion rules modeled after C). Thus, Checked!int is a virtually drop-in replacement for int useable in debug builds, to be replaced by int in release mode if efficiency demands it. Checked has customizable behavior with the help of a second type parameter, Hook. Depending on what methods Hook defines, core operations on the underlying integral may be verified for overflow or completely redefined. If Hook defines no method at all and carries no state, there is no change in behavior, i.e. Checked!(int, void) is a wrapper around int that adds no customization at all. This module provides a few predefined hooks (below) that add useful behavior to Checked:
Abort | fails every incorrect operation with a message to std.stdio. stderr followed by a call to assert(0). It is the default second parameter, i.e. Checked!short is the same as Checked!(short, Abort). |
Throw | fails every incorrect operation by throwing an exception. |
Warn | prints incorrect operations to std.stdio.stderr but otherwise preserves the built-in behavior. |
ProperCompare | fixes the comparison operators ==, !=, <, <=, >, and >= to return correct results in all circumstances, at a slight cost in efficiency. For example, Checked!(uint, ProperCompare)(1) > -1 is true, which is not the case for the built-in comparison. Also, comparing numbers for equality with floating-point numbers only passes if the integral can be converted to the floating-point number precisely, so as to preserve transitivity of equality. |
WithNaN | reserves a special "Not a Number" (NaN) value akin to the homonym value reserved for floating-point values. Once a Checked!(X, WithNaN) gets this special value, it preserves and propagates it until reassigned. isNaN can be used to query whether the object is not a number. |
Saturate | implements saturating arithmetic, i.e. Checked!(int, Saturate) "stops" at int.max for all operations that would cause an int to overflow toward infinity, and at int.min for all operations that would correspondingly overflow toward negative infinity. |
Checked!(Checked!int, ProperCompare) |
defines an int with fixed comparison operators that will fail with assert(0) upon overflow. (Recall that Abort is the default policy.) The order in which policies are combined is important because the outermost policy (ProperCompare in this case) has the first crack at intercepting an operator. The converse combination Checked!(Checked!(int, ProperCompare)) is meaningless because Abort will intercept comparison and will fail without giving ProperCompare a chance to intervene. |
Checked!(Checked!(int, ProperCompare), WithNaN) |
defines an int-like type that supports a NaN value. For values that are not NaN, comparison works properly. Again the composition order is important; Checked!(Checked!(int, WithNaN), ProperCompare) does not have good semantics because ProperCompare intercepts comparisons before the numbers involved are tested for NaN. |
Hook member | Semantics in Checked!(T, Hook) |
---|---|
defaultValue | If defined, Hook.defaultValue!T is used as the default initializer of the payload. |
min | If defined, Hook.min!T is used as the minimum value of the payload. |
max | If defined, Hook.max!T is used as the maximum value of the payload. |
hookOpCast | If defined, hook.hookOpCast!U(get) is forwarded to unconditionally when the payload is to be cast to type U. |
onBadCast | If defined and hookOpCast is not defined, onBadCast!U(get) is forwarded to when the payload is to be cast to type U and the cast would lose information or force a change of sign. |
hookOpEquals | If defined, hook.hookOpEquals(get, rhs) is forwarded to unconditionally when the payload is compared for equality against value rhs of integral, floating point, or Boolean type. |
hookOpCmp | If defined, hook.hookOpCmp(get, rhs) is forwarded to unconditionally when the payload is compared for ordering against value rhs of integral, floating point, or Boolean type. |
hookOpUnary | If defined, hook.hookOpUnary!op(get) (where op is the operator symbol) is forwarded to for unary operators - and ~. In addition, for unary operators ++ and --, hook.hookOpUnary!op(payload) is called, where payload is a reference to the value wrapped by Checked so the hook can change it. |
hookOpBinary | If defined, hook.hookOpBinary!op(get, rhs) (where op is the operator symbol and rhs is the right-hand side operand) is forwarded to unconditionally for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>>. |
hookOpBinaryRight | If defined, hook.hookOpBinaryRight!op(lhs, get) (where op is the operator symbol and lhs is the left-hand side operand) is forwarded to unconditionally for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>>. |
onOverflow | If defined, hook.onOverflow!op(get) is forwarded to for unary operators that overflow but only if hookOpUnary is not defined. Unary ~ does not overflow; unary - overflows only when the most negative value of a signed type is negated, and the result of the hook call is returned. When the increment or decrement operators overflow, the payload is assigned the result of hook.onOverflow!op(get). When a binary operator overflows, the result of hook.onOverflow!op(get, rhs) is returned, but only if Hook does not define hookOpBinary. |
hookOpOpAssign | If defined, hook.hookOpOpAssign!op(payload, rhs) (where op is the operator symbol and rhs is the right-hand side operand) is forwarded to unconditionally for binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>=. |
onLowerBound | If defined, hook.onLowerBound(value, bound) (where value is the value being assigned) is forwarded to when the result of binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>= is smaller than the smallest value representable by T. |
onUpperBound | If defined, hook.onUpperBound(value, bound) (where value is the value being assigned) is forwarded to when the result of binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>= is larger than the largest value representable by T. |
hookToHash | If defined, hook.hookToHash(payload) (where payload is a reference to the value wrapped by Checked) is forwarded to when toHash is called on a Checked type. Custom hashing can be implemented in a Hook, otherwise the built-in hashing is used. |
Examples:
int[] concatAndAdd(int[] a, int[] b, int offset) { // Aborts on overflow on size computation auto r = new int[(checked(a.length) + b.length).get]; // Aborts on overflow on element computation foreach (i; 0 .. a.length) r[i] = (a[i] + checked(offset)).get; foreach (i; 0 .. b.length) r[i + a.length] = (b[i] + checked(offset)).get; return r; } writeln(concatAndAdd([1, 2, 3], [4, 5], -1)); // [0, 1, 2, 3, 4]
Examples:
Saturate stops at an overflow
auto x = (cast(byte) 127).checked!Saturate; writeln(x); // 127 x++; writeln(x); // 127
Examples:
WithNaN has a special "Not a Number" (NaN) value akin to the homonym value reserved for floating-point values
auto x = 100.checked!WithNaN; writeln(x); // 100 x /= 0; assert(x.isNaN);
Examples:
ProperCompare fixes the comparison operators ==, !=, <, <=, >, and >= to return correct results
uint x = 1; auto y = x.checked!ProperCompare; assert(x < -1); // built-in comparison assert(y > -1); // ProperCompare
Examples:
Throw fails every incorrect operation by throwing an exception
import std.exception : assertThrown; auto x = -1.checked!Throw; assertThrown(x / 0); assertThrown(x + int.min); assertThrown(x == uint.max);
- struct
Checked
(T, Hook = Abort) if (isIntegral!T || is(T ==Checked
!(U, H), U, H)); - Checked integral type wraps an integral T and customizes its behavior with the help of a Hook type. The type wrapped must be one of the predefined integrals (unqualified), or another instance of
Checked
.- alias
Representation
= T; - The type of the integral subject to checking.
- Hook
hook
; hook
is a member variable if it has state, or an alias for Hook otherwise.- inout auto
get
(); - Returns a copy of the underlying value.Examples:
auto x = checked(ubyte(42)); static assert(is(typeof(x.get()) == ubyte)); writeln(x.get); // 42 const y = checked(ubyte(42)); static assert(is(typeof(y.get()) == const ubyte)); writeln(y.get); // 42
- enum Checked!(T, Hook)
min
;
enum Checked!(T, Hook)max
; - Defines the minimum and maximum. These values are hookable by defining Hook.
min
and/or Hook.max
.Examples:Defines the minimum and maximum. These values are hookable by defining Hook.min
and/or Hook.max
.writeln(Checked!short.min); // -32768 writeln(Checked!(short, WithNaN).min); // -32767 writeln(Checked!(uint, WithNaN).max); // uint.max - 1
- this(U)(U
rhs
)
if (valueConvertible!(U, T) || !isIntegral!T && is(typeof(T(rhs
))) || is(U == Checked!(V, W), V, W) && is(typeof(Checked!(T, Hook)(rhs
.get)))); - Constructor taking a value properly convertible to the underlying type. U may be either an integral that can be converted to T without a loss, or another Checked instance whose representation may be in turn converted to T without a loss.Examples:
auto a = checked(42L); writeln(a); // 42 auto b = Checked!long(4242); // convert 4242 to long writeln(b); // 4242
- ref Checked
opAssign
(U)(Urhs
) return
if (is(typeof(Checked!(T, Hook)(rhs
)))); - Assignment operator. Has the same constraints as the constructor.Examples:
Checked!long a; a = 42L; writeln(a); // 42 a = 4242; writeln(a); // 4242
Examples:Checked!long a, b; a = b = 3; assert(a == 3 && b == 3);
- this(Range)(Range
str
)
if (isInputRange!Range && isSomeChar!(ElementType!Range)); - Construct from a decimal string. The conversion follows the same rules as std.conv.to converting a string to the wrapped T type.Parameters:
Range str
an input range of characters Examples:std.conv.to can convert a string to a Checked!T:import std.conv : to; const a = to!long("1234"); const b = to!(Checked!long)("1234"); writeln(a); // b
- U
opCast
(U, this _)()
if (isIntegral!U || isFloatingPoint!U || is(U == bool)); - Casting operator to integral, bool, or floating point type. If Hook defines hookOpCast, the call immediately returns hook.hookOpCast!U(get). Otherwise, casting to bool yields get != 0 and casting to another integral that can represent all values of T returns get promoted to U.If a cast to a floating-point type is requested and Hook defines onBadCast, the cast is verified by ensuring get == cast(T) U(get). If that is not true, hook.onBadCast!U(get) is returned. If a cast to an integral type is requested and Hook defines onBadCast, the cast is verified by ensuring get and cast(U) get are the same arithmetic number. (Note that int(-1) and uint(1) are different values arithmetically although they have the same bitwise representation and compare equal by language rules.) If the numbers are not arithmetically equal, hook.onBadCast!U(get) is returned.Examples:
writeln(cast(uint)checked(42)); // 42 writeln(cast(uint)checked!WithNaN(-42)); // uint.max
- bool
opEquals
(U, this _)(Urhs
)
if (isIntegral!U || isFloatingPoint!U || is(U == bool) || is(U == Checked!(V, W), V, W) && is(typeof(this ==rhs
.payload))); - Compares this against
rhs
for equality. If Hook defines hookOpEquals, the function forwards to hook.hookOpEquals(get, rhs). Otherwise, the result of the built-in operation get == rhs is returned.If U is also an instance of Checked, both hooks (left- and right-hand side) are introspected for the method hookOpEquals. If both define it, priority is given to the left-hand side.Examples:import std.traits : isUnsigned; static struct MyHook { static bool thereWereErrors; static bool hookOpEquals(L, R)(L lhs, R rhs) { if (lhs != rhs) return false; static if (isUnsigned!L && !isUnsigned!R) { if (lhs > 0 && rhs < 0) thereWereErrors = true; } else static if (isUnsigned!R && !isUnsigned!L) if (lhs < 0 && rhs > 0) thereWereErrors = true; // Preserve built-in behavior. return true; } } auto a = checked!MyHook(-42); writeln(a); // uint(-42) assert(MyHook.thereWereErrors); MyHook.thereWereErrors = false; writeln(checked!MyHook(uint(-42))); // -42 assert(MyHook.thereWereErrors); static struct MyHook2 { static bool hookOpEquals(L, R)(L lhs, R rhs) { return lhs == rhs; } } MyHook.thereWereErrors = false; writeln(checked!MyHook2(uint(-42))); // a // Hook on left hand side takes precedence, so no errors assert(!MyHook.thereWereErrors);
- const nothrow @safe size_t
toHash
();
shared const nothrow @safe size_ttoHash
(this _)(); - Generates a hash for this. If Hook defines hookToHash, the call immediately returns hook.hookToHash(payload). If Hook does not implement hookToHash, but it has state, a hash will be generated for the Hook using the built-in function and it will be xored with the hash of the payload.
- const void
toString
(Writer, Char)(ref scope Writersink
, ref scope const FormatSpec!Charfmt
); - Writes a string representation of this to a
sink
.Parameters:Writer sink
A Char accepting output range. FormatSpec!Char fmt
A std.format.FormatSpec which controls how this is formatted. Examples:toString
is rarely directly invoked; the usual way of using it is via std.format.format:import std.format; writeln(format("%04d", checked(15))); // "0015" writeln(format("0x%02x", checked(15))); // "0x0f"
- auto
opCmp
(U, this _)(const Urhs
)
if (isIntegral!U || isFloatingPoint!U || is(U == bool));
autoopCmp
(U, Hook1, this _)(Checked!(U, Hook1)rhs
); - Compares this against
rhs
for ordering. If Hook defines hookOpCmp, the function forwards to hook.hookOpCmp(get, rhs). Otherwise, the result of the built-in comparison operation is returned.If U is also an instance of Checked, both hooks (left- and right-hand side) are introspected for the method hookOpCmp. If both define it, priority is given to the left-hand side.Examples:import std.traits : isUnsigned; static struct MyHook { static bool thereWereErrors; static int hookOpCmp(L, R)(L lhs, R rhs) { static if (isUnsigned!L && !isUnsigned!R) { if (rhs < 0 && rhs >= lhs) thereWereErrors = true; } else static if (isUnsigned!R && !isUnsigned!L) { if (lhs < 0 && lhs >= rhs) thereWereErrors = true; } // Preserve built-in behavior. return lhs < rhs ? -1 : lhs > rhs; } } auto a = checked!MyHook(-42); assert(a > uint(42)); assert(MyHook.thereWereErrors); static struct MyHook2 { static int hookOpCmp(L, R)(L lhs, R rhs) { // Default behavior return lhs < rhs ? -1 : lhs > rhs; } } MyHook.thereWereErrors = false; assert(Checked!(uint, MyHook2)(uint(-42)) <= a); //assert(Checked!(uint, MyHook2)(uint(-42)) >= a); // Hook on left hand side takes precedence, so no errors assert(!MyHook.thereWereErrors); assert(a <= Checked!(uint, MyHook2)(uint(-42))); assert(MyHook.thereWereErrors);
- auto
opUnary
(string op, this _)()
if (op == "+" || op == "-" || op == "~");
ref CheckedopUnary
(string op)() return
if (op == "++" || op == "--"); - Defines unary operators +, -, ~, ++, and --. Unary + is not overridable and always has built-in behavior (returns this). For the others, if Hook defines hookOpUnary,
opUnary
forwards to Checked!(typeof(hook.hookOpUnary!op(get)), Hook)(hook.hookOpUnary!op(get)).If Hook does not define hookOpUnary but defines onOverflow,opUnary
forwards to hook.onOverflow!op(get) in case an overflow occurs. For ++ and --, the payload is assigned from the result of the call to onOverflow. Note that unary - is considered to overflow if T is a signed integral of 32 or 64 bits and is equal to the most negative value. This is because that value has no positive negation.Examples:static struct MyHook { static bool thereWereErrors; static L hookOpUnary(string x, L)(L lhs) { if (x == "-" && lhs == -lhs) thereWereErrors = true; return -lhs; } } auto a = checked!MyHook(long.min); writeln(a); // -a assert(MyHook.thereWereErrors); auto b = checked!void(42); writeln(++b); // 43
- auto
opBinary
(string op, Rhs)(const Rhsrhs
)
if (isIntegral!Rhs || isFloatingPoint!Rhs || is(Rhs == bool));
const autoopBinary
(string op, Rhs)(const Rhsrhs
)
if (isIntegral!Rhs || isFloatingPoint!Rhs || is(Rhs == bool));
autoopBinary
(string op, U, Hook1)(Checked!(U, Hook1)rhs
);
const autoopBinary
(string op, U, Hook1)(Checked!(U, Hook1)rhs
); - Defines binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>>. If Hook defines hookOpBinary,
opBinary
forwards to Checked!(typeof(hook.hookOpBinary!op(get, rhs)), Hook)(hook.hookOpBinary!op(get, rhs)).If Hook does not define hookOpBinary but defines onOverflow,opBinary
forwards to hook.onOverflow!op(get,rhs
) in case an overflow occurs. If two Checked instances are involved in a binary operation and both define hookOpBinary, the left-hand side hook has priority. If both define onOverflow, a compile-time error occurs. - auto
opBinaryRight
(string op, Lhs)(const Lhslhs
)
if (isIntegral!Lhs || isFloatingPoint!Lhs || is(Lhs == bool));
const autoopBinaryRight
(string op, Lhs)(const Lhslhs
)
if (isIntegral!Lhs || isFloatingPoint!Lhs || is(Lhs == bool)); - Defines binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>> for the case when a built-in numeric or Boolean type is on the left-hand side, and a Checked instance is on the right-hand side.
- ref Checked
opOpAssign
(string op, Rhs)(const Rhsrhs
) return
if (isIntegral!Rhs || isFloatingPoint!Rhs || is(Rhs == bool));
ref CheckedopOpAssign
(string op, Rhs)(const Rhsrhs
) return
if (is(Rhs == Checked!(RhsT, RhsHook), RhsT, RhsHook)); - Defines operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>=.If Hook defines hookOpOpAssign,
opOpAssign
forwards to hook.hookOpOpAssign!op(payload,rhs
), where payload is a reference to the internally held data so the hook can change it. Otherwise, the operator first evaluates auto result = opBinary!op(payload, rhs).payload, which is subject to the hooks in opBinary. Then, if result is less than Checked!(T, Hook).min and if Hook defines onLowerBound, the payload is assigned from hook.onLowerBound(result, min). If result is greater than Checked!(T, Hook).max and if Hook defines onUpperBound, the payload is assigned from hook.onUpperBound(result, min). If the right-hand side is also a Checked but with a different hook or underlying type, the hook and underlying type of this Checked takes precedence. In all other cases, the built-in behavior is carried out.Parameters:op The operator involved (without the "=", e.g. "+" for "+=" etc) Rhs rhs
The right-hand side of the operator (left-hand side is this) Returns:A reference to this.Examples:static struct MyHook { static bool thereWereErrors; static T onLowerBound(Rhs, T)(Rhs rhs, T bound) { thereWereErrors = true; return bound; } static T onUpperBound(Rhs, T)(Rhs rhs, T bound) { thereWereErrors = true; return bound; } } auto x = checked!MyHook(byte.min); x -= 1; assert(MyHook.thereWereErrors); MyHook.thereWereErrors = false; x = byte.max; x += 1; assert(MyHook.thereWereErrors);
- Checked!(T, Hook)
checked
(Hook = Abort, T)(const Tvalue
)
if (is(typeof(Checked!(T, Hook)(value
)))); - Convenience function that turns an integral into the corresponding Checked instance by using template argument deduction. The hook type may be specified (by default Abort).Examples:
static assert(is(typeof(checked(42)) == Checked!int)); writeln(checked(42)); // Checked!int(42) static assert(is(typeof(checked!WithNaN(42)) == Checked!(int, WithNaN))); writeln(checked!WithNaN(42)); // Checked!(int, WithNaN)(42)
- struct
Abort
; - Force all integral errors to fail by printing an error message to stderr and then abort the program.
Abort
is the default second argument for Checked.- Dst
onBadCast
(Dst, Src)(Srcsrc
); - Called automatically upon a bad cast (one that loses precision or attempts to convert a negative value to an unsigned type). The source type is Src and the destination type is Dst.Parameters:
Src src
The source of the cast Returns:Nominally the result is the desired value of the cast operation, which will be forwarded as the result of the cast. For Abort, the function never returns because it aborts the program. - T
onLowerBound
(Rhs, T)(Rhsrhs
, Tbound
);
TonUpperBound
(Rhs, T)(Rhsrhs
, Tbound
); - Called automatically upon a bounds error.Parameters:
Rhs rhs
The right-hand side value in the assignment, after the operator has been evaluated T bound
The value of the bound being violated Returns:Nominally the result is the desired value of the operator, which will be forwarded as result. For Abort, the function never returns because it aborts the program. - bool
hookOpEquals
(Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon a comparison for equality. In case of a erroneous comparison (one that would make a signed negative value appear equal to an unsigned positive value), this hook issues assert(0) which terminates the application.Parameters:
Lhs lhs
The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int Rhs rhs
The right-hand side type involved in the operator Returns:Upon a correct comparison, returns the result of the comparison. Otherwise, the function terminates the application so it never returns. - int
hookOpCmp
(Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon a comparison for ordering using one of the operators <, <=, >, or >=. In case the comparison is erroneous (i.e. it would make a signed negative value appear greater than or equal to an unsigned positive value), then application is terminated with assert(0). Otherwise, the three-state result is returned (positive if lhs > rhs, negative if lhs < rhs, 0 otherwise).Parameters:
Lhs lhs
The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int Rhs rhs
The right-hand side type involved in the operator Returns:For correct comparisons, returns a positive integer if lhs > rhs, a negative integer if lhs < rhs, 0 if the two are equal. Upon a mistaken comparison such as int(-1) < uint(0), the function never returns because it aborts the program. - typeof(~Lhs())
onOverflow
(string x, Lhs)(Lhslhs
);
typeof(Lhs() + Rhs())onOverflow
(string x, Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon an overflow during a unary or binary operation.Parameters:
x The operator, e.g. - Lhs lhs
The left-hand side (or sole) argument Rhs rhs
The right-hand side type involved in the operator Returns:Nominally the result is the desired value of the operator, which will be forwarded as result. For Abort, the function never returns because it aborts the program.
- struct
Throw
; - Force all integral errors to fail by throwing an exception of type
Throw
.CheckFailure. The message coming with the error is similar to the one printed by Warn.Examples:void test(T)() { Checked!(int, Throw) x; x = 42; auto x1 = cast(T) x; writeln(x1); // 42 x = T.max + 1; import std.exception : assertThrown, assertNotThrown; assertThrown(cast(T) x); x = x.max; assertThrown(x += 42); assertThrown(x += 42L); x = x.min; assertThrown(-x); assertThrown(x -= 42); assertThrown(x -= 42L); x = -1; assertNotThrown(x == -1); assertThrown(x == uint(-1)); assertNotThrown(x <= -1); assertThrown(x <= uint(-1)); } test!short; test!(const short); test!(immutable short);
- class
CheckFailure
: object.Exception; - Exception type thrown upon any failure.
- Dst
onBadCast
(Dst, Src)(Srcsrc
); - Called automatically upon a bad cast (one that loses precision or attempts to convert a negative value to an unsigned type). The source type is Src and the destination type is Dst.Parameters:
Src src
The source of the cast Returns:Nominally the result is the desired value of the cast operation, which will be forwarded as the result of the cast. For Throw, the function never returns because it throws an exception. - T
onLowerBound
(Rhs, T)(Rhsrhs
, Tbound
);
TonUpperBound
(Rhs, T)(Rhsrhs
, Tbound
); - Called automatically upon a bounds error.Parameters:
Rhs rhs
The right-hand side value in the assignment, after the operator has been evaluated T bound
The value of the bound being violated Returns:Nominally the result is the desired value of the operator, which will be forwarded as result. For Throw, the function never returns because it throws. - bool
hookOpEquals
(L, R)(Llhs
, Rrhs
); - Called automatically upon a comparison for equality. Throws upon an erroneous comparison (one that would make a signed negative value appear equal to an unsigned positive value).Parameters:
L lhs
The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int R rhs
The right-hand side type involved in the operator Returns:The result of the comparison.Throws:CheckFailure if the comparison is mathematically erroneous. - int
hookOpCmp
(Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon a comparison for ordering using one of the operators <, <=, >, or >=. In case the comparison is erroneous (i.e. it would make a signed negative value appear greater than or equal to an unsigned positive value), throws a Throw.CheckFailure exception. Otherwise, the three-state result is returned (positive if lhs > rhs, negative if lhs < rhs, 0 otherwise).Parameters:
Lhs lhs
The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int Rhs rhs
The right-hand side type involved in the operator Returns:For correct comparisons, returns a positive integer if lhs > rhs, a negative integer if lhs < rhs, 0 if the two are equal.Throws:Upon a mistaken comparison such as int(-1) < uint(0), the function never returns because it throws a Throw.CheckedFailure exception. - typeof(~Lhs())
onOverflow
(string x, Lhs)(Lhslhs
);
typeof(Lhs() + Rhs())onOverflow
(string x, Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon an overflow during a unary or binary operation.Parameters:
x The operator, e.g. - Lhs lhs
The left-hand side (or sole) argument Rhs rhs
The right-hand side type involved in the operator Returns:Nominally the result is the desired value of the operator, which will be forwarded as result. For Throw, the function never returns because it throws an exception.
- struct
Warn
; - Hook that prints to stderr a trace of all integral errors, without affecting default behavior.Examples:
auto x = checked!Warn(42); short x1 = cast(short) x; //x += long(int.max); auto y = checked!Warn(cast(const int) 42); short y1 = cast(const byte) y;
- Dst
onBadCast
(Dst, Src)(Srcsrc
); - Called automatically upon a bad cast from
src
to type Dst (one that loses precision or attempts to convert a negative value to an unsigned type).Parameters:Src src
The source of the cast Dst The target type of the cast Returns:cast(Dst)src
- Lhs
onLowerBound
(Rhs, T)(Rhsrhs
, Tbound
);
TonUpperBound
(Rhs, T)(Rhsrhs
, Tbound
); - Called automatically upon a bad opOpAssign call (one that loses precision or attempts to convert a negative value to an unsigned type).Parameters:
Rhs rhs
The right-hand side value in the assignment, after the operator has been evaluated T bound
The bound being violated Returns:cast(Lhs)rhs
- bool
hookOpEquals
(Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon a comparison for equality. In case of an Erroneous comparison (one that would make a signed negative value appear equal to an unsigned positive value), writes a warning message to stderr as a side effect.Parameters:
Lhs lhs
The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int Rhs rhs
The right-hand side type involved in the operator Returns:In all cases the function returns the built-in result of lhs == rhs.Examples:auto x = checked!Warn(-42); // Passes writeln(x); // -42 // Passes but prints a warning // assert(x == uint(-42));
- int
hookOpCmp
(Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon a comparison for ordering using one of the operators <, <=, >, or >=. In case the comparison is erroneous (i.e. it would make a signed negative value appear greater than or equal to an unsigned positive value), then a warning message is printed to stderr.Parameters:
Lhs lhs
The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int Rhs rhs
The right-hand side type involved in the operator Returns:In all cases, returns lhs < rhs ? -1 : lhs > rhs. The result is not autocorrected in case of an erroneous comparison.Examples:auto x = checked!Warn(-42); // Passes assert(x <= -42); // Passes but prints a warning // assert(x <= uint(-42));
- typeof(~Lhs())
onOverflow
(string x, Lhs)(ref Lhslhs
);
typeof(Lhs() + Rhs())onOverflow
(string x, Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Called automatically upon an overflow during a unary or binary operation.Parameters:
x The operator involved Lhs The first argument of Checked, e.g. int if the left-hand side of the operator is Checked!int Rhs The right-hand side type involved in the operator Returns:mixin(x ~ "lhs") for unary, mixin("lhs" ~ x ~ "rhs") for binary
- struct
ProperCompare
; - Hook that provides arithmetically correct comparisons for equality and ordering. Comparing an object of type Checked!(X, ProperCompare) against another integral (for equality or ordering) ensures that no surprising conversions from signed to unsigned integral occur before the comparison. Using Checked!(X, ProperCompare) on either side of a comparison for equality against a floating-point number makes sure the integral can be properly converted to the floating point type, thus making sure equality is transitive.Examples:
alias opEqualsProper = ProperCompare.hookOpEquals; assert(opEqualsProper(42, 42)); assert(opEqualsProper(42.0, 42.0)); assert(opEqualsProper(42u, 42)); assert(opEqualsProper(42, 42u)); writeln(-1); // 4294967295u assert(!opEqualsProper(-1, 4294967295u)); assert(!opEqualsProper(const uint(-1), -1)); assert(!opEqualsProper(uint(-1), -1.0)); writeln(3_000_000_000U); // -1_294_967_296 assert(!opEqualsProper(3_000_000_000U, -1_294_967_296));
- bool
hookOpEquals
(L, R)(Llhs
, Rrhs
); - Hook for == and != that ensures comparison against integral values has the behavior expected by the usual arithmetic rules. The built-in semantics yield surprising behavior when comparing signed values against unsigned values for equality, for example uint.max == -1 or -1_294_967_296 == 3_000_000_000u. The call hookOpEquals(x, y) returns true if and only if x and y represent the same arithmetic number.If one of the numbers is an integral and the other is a floating-point number, hookOpEquals(x, y) returns true if and only if the integral can be converted exactly (without approximation) to the floating-point number. This is in order to preserve transitivity of equality: if hookOpEquals(x, y) and hookOpEquals(y, z) then hookOpEquals(y, z), in case x, y, and z are a mix of integral and floating-point numbers.Parameters:
L lhs
The left-hand side of the comparison for equality R rhs
The right-hand side of the comparison for equality Returns:The result of the comparison, true if the values are equal - auto
hookOpCmp
(L, R)(Llhs
, Rrhs
); - Hook for <, <=, >, and >= that ensures comparison against integral values has the behavior expected by the usual arithmetic rules. The built-in semantics yield surprising behavior when comparing signed values against unsigned values, for example 0u < -1. The call hookOpCmp(x, y) returns -1 if and only if x is smaller than y in abstract arithmetic sense.If one of the numbers is an integral and the other is a floating-point number, hookOpEquals(x, y) returns a floating-point number that is -1 if x < y, 0 if x == y, 1 if x > y, and NaN if the floating-point number is NaN.Parameters:
L lhs
The left-hand side of the comparison for ordering R rhs
The right-hand side of the comparison for ordering Returns:The result of the comparison (negative if lhs < rhs, positive if lhs > rhs, 0 if the values are equal)
- struct
WithNaN
; - Hook that reserves a special value as a "Not a Number" representative. For signed integrals, the reserved value is T.min. For signed integrals, the reserved value is T.max.The default value of a Checked!(X, WithNaN) is its NaN value, so care must be taken that all variables are explicitly initialized. Any arithmetic and logic operation involving at least on NaN becomes NaN itself. All of a == b, a < b, a > b, a <= b, a >= b yield false if at least one of a and b is NaN.Examples:
auto x1 = Checked!(int, WithNaN)(); assert(x1.isNaN); writeln(x1.get); // int.min assert(x1 != x1); assert(!(x1 < x1)); assert(!(x1 > x1)); assert(!(x1 == x1)); ++x1; assert(x1.isNaN); writeln(x1.get); // int.min --x1; assert(x1.isNaN); writeln(x1.get); // int.min x1 = 42; assert(!x1.isNaN); writeln(x1); // x1 assert(x1 <= x1); assert(x1 >= x1); static assert(x1.min == int.min + 1); x1 += long(int.max);
- enum T
defaultValue
(T); - The default value used for values not explicitly initialized. It is the NaN value, i.e. T.min for signed integrals and T.max for unsigned integrals.
- enum T
max
(T);
enum Tmin
(T); - The maximum value representable is T.
max
for signed integrals, T.max - 1 for unsigned integrals. The minimum value representable is T.min + 1 for signed integrals, 0 for unsigned integrals. - Lhs
hookOpCast
(Lhs, Rhs)(Rhsrhs
); - If
rhs
is WithNaN.defaultValue!Rhs, returns WithNaN.defaultValue!Lhs. Otherwise, returns cast(Lhs) rhs.Parameters:Rhs rhs
the value being cast (Rhs is the first argument to Checked) Lhs the target type of the cast Returns:The result of the cast operation.Examples:auto x = checked!WithNaN(422); writeln((cast(ubyte)x)); // 255 x = checked!WithNaN(-422); writeln((cast(byte)x)); // -128 writeln(cast(short)x); // -422 assert(cast(bool) x); x = x.init; // set back to NaN assert(x != true); assert(x != false);
- bool
hookOpEquals
(Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Returns false if lhs == WithNaN.defaultValue!Lhs, lhs == rhs otherwise.Parameters:
Lhs lhs
The left-hand side of the comparison (Lhs is the first argument to Checked) Rhs rhs
The right-hand side of the comparison Returns:lhs
!= WithNaN.defaultValue!Lhs &&lhs
==rhs
- double
hookOpCmp
(Lhs, Rhs)(Lhslhs
, Rhsrhs
); - If lhs == WithNaN.defaultValue!Lhs, returns double.init. Otherwise, has the same semantics as the default comparison.Parameters:
Lhs lhs
The left-hand side of the comparison (Lhs is the first argument to Checked) Rhs rhs
The right-hand side of the comparison Returns:double.init iflhs
== WitnNaN.defaultValue!Lhs, -1.0 if lhs < rhs, 0.0 if lhs == rhs, 1.0 if lhs > rhs.Examples:Checked!(int, WithNaN) x; assert(!(x < 0) && !(x > 0) && !(x == 0)); x = 1; assert(x > 0 && !(x < 0) && !(x == 0));
- auto
hookOpUnary
(string x, T)(ref Tv
); - Defines hooks for unary operators -, ~, ++, and --.For - and ~, if v == WithNaN.defaultValue!T, returns WithNaN.defaultValue!T. Otherwise, the semantics is the same as for the built-in operator. For ++ and --, if v == WithNaN.defaultValue!Lhs or the operation would result in an overflow, sets
v
to WithNaN.defaultValue!T. Otherwise, the semantics is the same as for the built-in operator.Parameters:x The operator symbol T v
The left-hand side of the comparison (T is the first argument to Checked) Returns:- For x == "-" || x == "~": If v == WithNaN.defaultValue!T, the function returns WithNaN.defaultValue!T. Otherwise it returns the normal result of the operator.
- For x == "++" || x == "--": The function returns void.
Examples:Checked!(int, WithNaN) x; ++x; assert(x.isNaN); x = 1; assert(!x.isNaN); x = -x; ++x; assert(!x.isNaN);
- auto
hookOpBinary
(string x, L, R)(Llhs
, Rrhs
); - Defines hooks for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>> for cases where a Checked object is the left-hand side operand. If lhs == WithNaN.defaultValue!Lhs, returns WithNaN.defaultValue!(typeof(lhs + rhs)) without evaluating the operand. Otherwise, evaluates the operand. If evaluation does not overflow, returns the result. Otherwise, returns WithNaN.defaultValue!(typeof(lhs + rhs)).Parameters:
x The operator symbol L lhs
The left-hand side operand (Lhs is the first argument to Checked) R rhs
The right-hand side operand Returns:If lhs != WithNaN.defaultValue!Lhs and the operator does not overflow, the function returns the same result as the built-in operator. In all other cases, returns WithNaN.defaultValue!(typeof(lhs + rhs)).Examples:Checked!(int, WithNaN) x; assert((x + 1).isNaN); x = 100; assert(!(x + 1).isNaN);
- auto
hookOpBinaryRight
(string x, L, R)(Llhs
, Rrhs
); - Defines hooks for binary operators +, -, *, /, %, ^^, &, |, ^, <<, >>, and >>> for cases where a Checked object is the right-hand side operand. If rhs == WithNaN.defaultValue!Rhs, returns WithNaN.defaultValue!(typeof(lhs + rhs)) without evaluating the operand. Otherwise, evaluates the operand. If evaluation does not overflow, returns the result. Otherwise, returns WithNaN.defaultValue!(typeof(lhs + rhs)).Parameters:
x The operator symbol L lhs
The left-hand side operand R rhs
The right-hand side operand (Rhs is the first argument to Checked) Returns:If rhs != WithNaN.defaultValue!Rhs and the operator does not overflow, the function returns the same result as the built-in operator. In all other cases, returns WithNaN.defaultValue!(typeof(lhs + rhs)).Examples:Checked!(int, WithNaN) x; assert((1 + x).isNaN); x = 100; assert(!(1 + x).isNaN);
- void
hookOpOpAssign
(string x, L, R)(ref Llhs
, Rrhs
); - Defines hooks for binary operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>= for cases where a Checked object is the left-hand side operand. If lhs == WithNaN.defaultValue!Lhs, no action is carried. Otherwise, evaluates the operand. If evaluation does not overflow and fits in Lhs without loss of information or change of sign, sets
lhs
to the result. Otherwise, setslhs
to WithNaN.defaultValue!Lhs.Parameters:x The operator symbol (without the =) L lhs
The left-hand side operand (Lhs is the first argument to Checked) R rhs
The right-hand side operand Returns:voidExamples:Checked!(int, WithNaN) x; x += 4; assert(x.isNaN); x = 0; x += 4; assert(!x.isNaN); x += int.max; assert(x.isNaN);
- bool
isNaN
(T)(const Checked!(T, WithNaN)x
); - Queries whether a Checked!(T, WithNaN) object is not a number (NaN).Parameters:
Checked!(T, WithNaN) x
the Checked instance queried Returns:true ifx
is a NaN, false otherwiseExamples:auto x1 = Checked!(int, WithNaN)(); assert(x1.isNaN); x1 = 1; assert(!x1.isNaN); x1 = x1.init; assert(x1.isNaN);
- struct
Saturate
; - Hook that implements saturation, i.e. any arithmetic operation that would overflow leaves the result at its extreme value (min or max depending on the direction of the overflow).Saturation is not sticky; if a value reaches its saturation value, another operation may take it back to normal range.Examples:
auto x = checked!Saturate(int.max); ++x; writeln(x); // int.max --x; writeln(x); // int.max - 1 x = int.min; writeln(-x); // int.max x -= 42; writeln(x); // int.min writeln(x * -2); // int.max
- T
onLowerBound
(Rhs, T)(Rhsrhs
, Tbound
);
TonUpperBound
(Rhs, T)(Rhsrhs
, Tbound
); - Implements saturation for operators +=, -=, *=, /=, %=, ^^=, &=, |=, ^=, <<=, >>=, and >>>=. This hook is called if the result of the binary operation does not fit in Lhs without loss of information or a change in sign.Parameters:
Rhs The right-hand side type in the assignment, after the operation has been computed T bound
The bound being violated Returns:Lhs.max if rhs >= 0, Lhs.min otherwise.Examples:auto x = checked!Saturate(short(100)); x += 33000; writeln(x); // short.max x -= 70000; writeln(x); // short.min
- auto
onOverflow
(string x, Lhs)(Lhslhs
);
typeof(Lhs() + Rhs())onOverflow
(string x, Lhs, Rhs)(Lhslhs
, Rhsrhs
); - Implements saturation for operators +, - (unary and binary), *, /, %, ^^, &, |, ^, <<, >>, and >>>.For unary -,
onOverflow
is called if lhs == Lhs.min and Lhs is a signed type. The function returns Lhs.max. For binary operators, the result is as follows:- Lhs.max if the result overflows in the positive direction, on division by 0, or on shifting right by a negative value
- Lhs.min if the result overflows in the negative direction
- 0 if
lhs
is being shifted left by a negative value, or shifted right by a large positive value
Parameters:x The operator involved in the opAssign operation Lhs The left-hand side of the operator (Lhs is the first argument to Checked) Rhs The right-hand side type in the operator Returns:The saturated result of the operator.Examples:writeln(checked!Saturate(int.max) + 1); // int.max writeln(checked!Saturate(100)^^10); // int.max writeln(checked!Saturate(-100)^^10); // int.max writeln(checked!Saturate(100) / 0); // int.max writeln(checked!Saturate(100) << -1); // 0 writeln(checked!Saturate(100) << 33); // int.max writeln(checked!Saturate(100) >> -1); // int.max writeln(checked!Saturate(100) >> 33); // 0
- typeof(mixin(x == "cmp" ? "0" : "L() " ~ x ~ " R()"))
opChecked
(string x, L, R)(const Llhs
, const Rrhs
, ref booloverflow
)
if (isIntegral!L && isIntegral!R); - Defines binary operations with overflow checking for any two integral types. The result type obeys the language rules (even when they may be counterintuitive), and
overflow
is set if an overflow occurs (including inadvertent change of signedness, e.g. -1 is converted to uint). Conceptually the behavior is:- Perform the operation in infinite precision
- If the infinite-precision result fits in the result type, return it and
do not touch
overflow
- Otherwise, set
overflow
to true and return an unspecified value
Parameters:x The binary operator involved, e.g. / L lhs
The left-hand side of the operator R rhs
The right-hand side of the operator bool overflow
The overflow indicator (assigned true in case there's an error) Returns:The result of the operation, which is the same as the built-in operatorExamples:bool overflow; assert(opChecked!"+"(const short(1), short(1), overflow) == 2 && !overflow); assert(opChecked!"+"(1, 1, overflow) == 2 && !overflow); assert(opChecked!"+"(1, 1u, overflow) == 2 && !overflow); assert(opChecked!"+"(-1, 1u, overflow) == 0 && !overflow); assert(opChecked!"+"(1u, -1, overflow) == 0 && !overflow);
Examples:bool overflow; assert(opChecked!"-"(1, 1, overflow) == 0 && !overflow); assert(opChecked!"-"(1, 1u, overflow) == 0 && !overflow); assert(opChecked!"-"(1u, -1, overflow) == 2 && !overflow); assert(opChecked!"-"(-1, 1u, overflow) == 0 && overflow);
Copyright © 1999-2022 by the D Language Foundation | Page generated by
Ddoc on (no date time)