Function std.algorithm.comparison.castSwitch
Executes and returns one of a collection of handlers based on the type of the switch object.
The first choice that switchObject
can be casted to the type
of argument it accepts will be called with switchObject
casted to that
type, and the value it'll return will be returned by castSwitch
.
If a choice's return type is void, the choice must throw an exception, unless all the choices are void. In that case, castSwitch itself will return void.
Throws
If none of the choice matches, a SwitchError
will be thrown. SwitchError
will also be thrown if not all the choices are void and a void
choice was executed without throwing anything.
Parameters
Returns
The value of the selected choice.
Note
castSwitch
can only be used with object types.
Example
import std .algorithm .iteration : map;
import std .format : format;
class A
{
int a;
this(int a) {this .a = a;}
@property int i() { return a; }
}
interface I { }
class B : I { }
Object[] arr = [new A(1), new B(), null];
auto results = arr .map!(castSwitch!(
(A a) => "A with a value of %d" .format(a .a),
(I i) => "derived from I",
() => "null reference",
))();
// A is handled directly:
writeln(results[0]); // "A with a value of 1"
// B has no handler - it is handled by the handler of I:
writeln(results[1]); // "derived from I"
// null is handled by the null handler:
writeln(results[2]); // "null reference"
Example
Using with void handlers:
import std .exception : assertThrown;
class A { }
class B { }
// Void handlers are allowed if they throw:
assertThrown!Exception(
new B() .castSwitch!(
(A a) => 1,
(B d) { throw new Exception("B is not allowed!"); }
)()
);
// Void handlers are also allowed if all the handlers are void:
new A() .castSwitch!(
(A a) { },
(B b) { assert(false); },
)();