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# std.algorithm.mutation

This is a submodule of std.algorithm.
It contains generic mutation algorithms.

Function Name | Description |
---|---|

bringToFront | If a = [1, 2, 3] and b = [4, 5, 6, 7], bringToFront(a, b) leaves a = [4, 5, 6] and b = [7, 1, 2, 3]. |

copy | Copies a range to another. If a = [1, 2, 3] and b = new int[5], then copy(a, b) leaves b = [1, 2, 3, 0, 0] and returns b[3 .. $]. |

fill | Fills a range with a pattern, e.g., if a = new int[3], then fill(a, 4) leaves a = [4, 4, 4] and fill(a, [3, 4]) leaves a = [3, 4, 3]. |

initializeAll | If a = [1.2, 3.4], then initializeAll(a) leaves a = [double.init, double.init]. |

move | move(a, b) moves a into b. move(a) reads a destructively. |

moveAll | Moves all elements from one range to another. |

moveSome | Moves as many elements as possible from one range to another. |

remove | Removes elements from a range in-place, and returns the shortened range. |

reverse | If a = [1, 2, 3], reverse(a) changes it to [3, 2, 1]. |

strip | Strips all leading and trailing elements equal to a value, or that satisfy a predicate. If a = [1, 1, 0, 1, 1], then strip(a, 1) and strip!(e => e == 1)(a) returns [0]. |

stripLeft | Strips all leading elements equal to a value, or that satisfy a predicate. If a = [1, 1, 0, 1, 1], then stripLeft(a, 1) and stripLeft!(e => e == 1)(a) returns [0, 1, 1]. |

stripRight | Strips all trailing elements equal to a value, or that satisfy a predicate. If a = [1, 1, 0, 1, 1], then stripRight(a, 1) and stripRight!(e => e == 1)(a) returns [1, 1, 0]. |

swap | Swaps two values. |

swapRanges | Swaps all elements of two ranges. |

uninitializedFill | Fills a range (assumed uninitialized) with a value. |

License:

Authors:

Source: std/algorithm/mutation.d

- size_t bringToFront(Range1, Range2)(Range1
*front*, Range2*back*) if (isInputRange!Range1 && isForwardRange!Range2); - The bringToFront function has considerable flexibility and usefulness. It can rotate elements in one buffer left or right, swap buffers of equal length, and even move elements across disjoint buffers of different types and different lengths.bringToFront takes two ranges
*front*and*back*, which may be of different types. Considering the concatenation of*front*and*back*one unified range, bringToFront rotates that unified range such that all elements in*back*are brought to the beginning of the unified range. The relative ordering of elements in*front*and*back*, respectively, remains unchanged. Performs Ο(max(*front*.length,*back*.length)) evaluations of swap.Preconditions: Either

*front*and*back*are disjoint, or*back*is reachable from*front*and*front*is not reachable from*back*.Returns:The number of elements brought to the*front*, i.e., the length of*back*.See Also:Examples:Examples:The*front*range may actually "step over" the*back*range. This is very useful with forward ranges that cannot compute comfortably right-bounded subranges like arr[0 .. 4] above. In the example below, r2 is a right subrange of r1.import std.algorithm.comparison : equal; import std.container : SList; auto list = SList!(int)(4, 5, 6, 7, 1, 2, 3); auto r1 = list[]; auto r2 = list[]; popFrontN(r2, 4); assert(equal(r2, [ 1, 2, 3 ])); bringToFront(r1, r2); assert(equal(list[], [ 1, 2, 3, 4, 5, 6, 7 ]));

Examples:Elements can be swapped across ranges of different types:import std.algorithm.comparison : equal; import std.container : SList; auto list = SList!(int)(4, 5, 6, 7); auto vec = [ 1, 2, 3 ]; bringToFront(list[], vec); assert(equal(list[], [ 1, 2, 3, 4 ])); assert(equal(vec, [ 5, 6, 7 ]));

- TargetRange copy(SourceRange, TargetRange)(SourceRange
*source*, TargetRange*target*) if (isInputRange!SourceRange && isOutputRange!(TargetRange, ElementType!SourceRange)); - Copies the content of
*source*into*target*and returns the remaining (unfilled) part of*target*.Preconditions:

*target*shall have enough room to accomodate the entirety of*source*.See Also:Examples:int[] a = [ 1, 5 ]; int[] b = [ 9, 8 ]; int[] buf = new int[](a.length + b.length + 10); auto rem = a.copy(buf); // copy a into buf rem = b.copy(rem); // copy b into remainder of buf assert(buf[0 .. a.length + b.length] == [1, 5, 9, 8]); assert(rem.length == 10); // unused slots in buf

Examples:As long as the*target*range elements support assignment from*source*range elements, different types of ranges are accepted:float[] src = [ 1.0f, 5 ]; double[] dest = new double[src.length]; src.copy(dest);

Examples:To copy at most n elements from a range, you may want to use std.range.take:import std.range; int[] src = [ 1, 5, 8, 9, 10 ]; auto dest = new int[](3); src.take(dest.length).copy(dest); assert(dest == [ 1, 5, 8 ]);

Examples:To copy just those elements from a range that satisfy a predicate, use filter:import std.algorithm.iteration : filter; int[] src = [ 1, 5, 8, 9, 10, 1, 2, 0 ]; auto dest = new int[src.length]; auto rem = src .filter!(a => (a & 1) == 1) .copy(dest); assert(dest[0 .. $ - rem.length] == [ 1, 5, 9, 1 ]);

Examples:std.range.retro can be used to achieve behavior similar to STL's copy_backward':import std.algorithm, std.range; int[] src = [1, 2, 4]; int[] dest = [0, 0, 0, 0, 0]; src.retro.copy(dest.retro); assert(dest == [0, 0, 1, 2, 4]);

- void fill(Range, Value)(Range
*range*, Value*value*) if (isInputRange!Range && is(typeof(*range*.front =*value*))); - Assigns
*value*to each element of input range*range*.Parameters:Range *range*An input range that exposes references to its elements and has assignable elements Value *value*Assigned to each element of *range*See Also:Examples:int[] a = [ 1, 2, 3, 4 ]; fill(a, 5); assert(a == [ 5, 5, 5, 5 ]);

- void fill(Range1, Range2)(Range1
*range*, Range2*filler*) if (isInputRange!Range1 && (isForwardRange!Range2 || isInputRange!Range2 && isInfinite!Range2) && is(typeof(Range1.init.front = Range2.init.front))); - Fills
*range*with a pattern copied from*filler*. The length of*range*does not have to be a multiple of the length of*filler*. If*filler*is empty, an exception is thrown.Parameters:Range1 *range*An input range that exposes references to its elements and has assignable elements. Range2 *filler*The forward range representing the fill pattern. Examples:int[] a = [ 1, 2, 3, 4, 5 ]; int[] b = [ 8, 9 ]; fill(a, b); assert(a == [ 8, 9, 8, 9, 8 ]);

- void initializeAll(Range)(Range
*range*) if (isInputRange!Range && hasLvalueElements!Range && hasAssignableElements!Range); - Initializes all elements of
*range*with their .init value. Assumes that the elements of the*range*are uninitialized.Parameters:Range *range*An input range that exposes references to its elements and has assignable elements See Also:Example:

struct S { ... } S[] s = (cast(S*) malloc(5 * S.sizeof))[0 .. 5]; initializeAll(s); assert(s == [ 0, 0, 0, 0, 0 ]);

- void move(T)(ref T
*source*, ref T*target*);

T move(T)(ref T*source*); - Moves
*source*into*target*via a destructive copy.Parameters:T *source*Data to copy. If a destructor or postblit is defined, it is reset to its .init value after it is moved into *target*. Note that data with internal pointers that point to itself cannot be moved, and will trigger an assertion failure.T *target*Where to copy into. The destructor, if any, is invoked before the copy is performed. Examples:Object obj1 = new Object; Object obj2 = obj1; Object obj3; move(obj2, obj3); assert(obj3 is obj1);

Examples:// Structs without destructors are simply copied struct S1 { int a = 1; int b = 2; } S1 s11 = { 10, 11 }; S1 s12; move(s11, s12); assert(s11.a == 10 && s11.b == 11 && s12.a == 10 && s12.b == 11); // But structs with destructors or postblits are reset to their .init value // after copying to the target. struct S2 { int a = 1; int b = 2; ~this() { } } S2 s21 = { 3, 4 }; S2 s22; move(s21, s22); assert(s21.a == 1 && s21.b == 2 && s22.a == 3 && s22.b == 4);

- Range2 moveAll(Range1, Range2)(Range1
*src*, Range2*tgt*) if (isInputRange!Range1 && isInputRange!Range2 && is(typeof(move(*src*.front,*tgt*.front)))); - For each element a in
*src*and each element b in*tgt*in lockstep in increasing order, calls move(a, b).Preconditions: walkLength(

*src*) <= walkLength(*tgt*). An exception will be thrown if this condition does not hold, i.e., there is not enough room in*tgt*to accommodate all of*src*.Parameters:Range1 *src*An input range with movable elements. Range2 *tgt*An input range with elements that elements from *src*can be moved into.Returns:The leftover portion of*tgt*after all elements from*src*have been moved.Examples:int[] a = [ 1, 2, 3 ]; int[] b = new int[5]; assert(moveAll(a, b) is b[3 .. $]); assert(a == b[0 .. 3]); assert(a == [ 1, 2, 3 ]);

- Tuple!(Range1, Range2) moveSome(Range1, Range2)(Range1
*src*, Range2*tgt*) if (isInputRange!Range1 && isInputRange!Range2 && is(typeof(move(*src*.front,*tgt*.front)))); - For each element a in
*src*and each element b in*tgt*in lockstep in increasing order, calls move(a, b). Stops when either*src*or*tgt*have been exhausted.Parameters:Range1 *src*An input range with movable elements. Range2 *tgt*An input range with elements that elements from *src*can be moved into.Returns:The leftover portions of the two ranges after one or the other of the ranges have been exhausted.Examples:int[] a = [ 1, 2, 3, 4, 5 ]; int[] b = new int[3]; assert(moveSome(a, b)[0] is a[3 .. $]); assert(a[0 .. 3] == b); assert(a == [ 1, 2, 3, 4, 5 ]);

- enum SwapStrategy: int;
- Defines the swapping strategy for algorithms that need to swap elements in a range (such as partition and sort). The strategy concerns the swapping of elements that are not the core concern of the algorithm. For example, consider an algorithm that sorts [ "abc", "b", "aBc" ] according to toUpper(a) < toUpper(b). That algorithm might choose to swap the two equivalent strings "abc" and "aBc". That does not affect the sorting since both [ "abc", "aBc", "b" ] and [ "aBc", "abc", "b" ] are valid outcomes.Some situations require that the algorithm must NOT ever change the relative ordering of equivalent elements (in the example above, only [ "abc", "aBc", "b" ] would be the correct result). Such algorithms are called
**stable**. If the ordering algorithm may swap equivalent elements discretionarily, the ordering is called**unstable**. Yet another class of algorithms may choose an intermediate tradeoff by being stable only on a well-defined subrange of the range. There is no established terminology for such behavior; this library calls it**semistable**. Generally, the stable ordering strategy may be more costly in time and/or space than the other two because it imposes additional constraints. Similarly, semistable may be costlier than unstable. As (semi-)stability is not needed very often, the ordering algorithms in this module parameterized by SwapStrategy all choose SwapStrategy.unstable as the default.- unstable
- Allows freely swapping of elements as long as the output satisfies the algorithm's requirements.
- semistable
- In algorithms partitioning ranges in two, preserve relative ordering of elements only to the left of the partition point.
- stable
- Preserve the relative ordering of elements to the largest extent allowed by the algorithm's requirements.

- Range remove(SwapStrategy s = SwapStrategy.stable, Range, Offset...)(Range
*range*, Offset*offset*) if (s != SwapStrategy.stable && isBidirectionalRange!Range && hasLvalueElements!Range && hasLength!Range && Offset.length >= 1); - Eliminates elements at given offsets from
*range*and returns the shortened*range*. In the simplest call, one element is removed.int[] a = [ 3, 5, 7, 8 ]; assert(remove(a, 1) == [ 3, 7, 8 ]); assert(a == [ 3, 7, 8, 8 ]);

In the case above the element at*offset*1 is removed and remove returns the*range*smaller by one element. The original array has remained of the same length because all functions in std.algorithm only change*content*, not*topology*. The value 8 is repeated because move was invoked to move elements around and on integers move simply copies the source to the destination. To replace a with the effect of the removal, simply assign a = remove(a, 1). The slice will be rebound to the shorter array and the operation completes with maximal efficiency. Multiple indices can be passed into remove. In that case, elements at the respective indices are all removed. The indices must be passed in increasing order, otherwise an exception occurs.int[] a = [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]; assert(remove(a, 1, 3, 5) == [ 0, 2, 4, 6, 7, 8, 9, 10 ]);

(Note how all indices refer to slots in the*original*array, not in the array as it is being progressively shortened.) Finally, any combination of integral offsets and tuples composed of two integral offsets can be passed in.int[] a = [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]; assert(remove(a, 1, tuple(3, 5), 9) == [ 0, 2, 6, 7, 8, 10 ]);

In this case, the slots at positions 1, 3, 4, and 9 are removed from the array. The tuple passes in a*range*closed to the left and open to the right (consistent with built-in slices), e.g. tuple(3, 5) means indices 3 and 4 but not 5. If the need is to remove some elements in the*range*but the order of the remaining elements does not have to be preserved, you may want to pass SwapStrategy.unstable to remove.int[] a = [ 0, 1, 2, 3 ]; assert(remove!(SwapStrategy.unstable)(a, 1) == [ 0, 3, 2 ]);

In the case above, the element at slot 1 is removed, but replaced with the last element of the*range*. Taking advantage of the relaxation of the stability requirement, remove moved elements from the end of the array over the slots to be removed. This way there is less data movement to be done which improves the execution time of the function. The function remove works on any forward*range*. The moving strategy is (listed from fastest to slowest):- If s ==
SwapStrategy.unstable && isRandomAccessRange!Range && hasLength!Range
&& hasLvalueElements!Range, then elements are moved from the end
of the
*range*into the slots to be filled. In this case, the absolute minimum of moves is performed. - Otherwise, if s ==
SwapStrategy.unstable && isBidirectionalRange!Range && hasLength!Range
&& hasLvalueElements!Range, then elements are still moved from the
end of the
*range*, but time is spent on advancing between slots by repeated calls to*range*.popFront. - Otherwise, elements are moved
incrementally towards the front of
*range*; a given element is never moved several times, but more elements are moved than in the previous cases.

- If s ==
SwapStrategy.unstable && isRandomAccessRange!Range && hasLength!Range
&& hasLvalueElements!Range, then elements are moved from the end
of the
- Range remove(alias pred, SwapStrategy s = SwapStrategy.stable, Range)(Range
*range*) if (isBidirectionalRange!Range && hasLvalueElements!Range); - Reduces the length of the bidirectional
*range**range*by removing elements that satisfy pred. If s = SwapStrategy.unstable, elements are moved from the right end of the*range*over the elements to eliminate. If s = SwapStrategy.stable (the default), elements are moved progressively to front such that their relative order is preserved. Returns the filtered*range*.Examples:static immutable base = [1, 2, 3, 2, 4, 2, 5, 2]; int[] arr = base[].dup; // using a string-based predicate assert(remove!("a == 2")(arr) == [ 1, 3, 4, 5 ]); // The original array contents have been modified, // so we need to reset it to its original state. // The length is unmodified however. arr[] = base[]; // using a lambda predicate assert(remove!(a => a == 2)(arr) == [ 1, 3, 4, 5 ]);

- void reverse(Range)(Range
*r*) if (isBidirectionalRange!Range && !isRandomAccessRange!Range && hasSwappableElements!Range);

void reverse(Range)(Range*r*) if (isRandomAccessRange!Range && hasLength!Range); - Reverses
*r*in-place. Performs*r*.length / 2 evaluations of swap.See Also:Examples:int[] arr = [ 1, 2, 3 ]; reverse(arr); assert(arr == [ 3, 2, 1 ]);

- void reverse(Char)(Char[]
*s*) if (isNarrowString!(Char[]) && !is(Char == const) && !is(Char == immutable)); - Reverses r in-place, where r is a narrow string (having elements of type char or wchar). UTF sequences consisting of multiple code units are preserved properly.Examples:
char[] arr = "hello\U00010143\u0100\U00010143".dup; reverse(arr); assert(arr == "\U00010143\u0100\U00010143olleh");

- Range strip(Range, E)(Range
*range*, E*element*) if (isBidirectionalRange!Range && is(typeof(*range*.front ==*element*) : bool));

Range strip(alias pred, Range)(Range*range*) if (isBidirectionalRange!Range && is(typeof(pred(*range*.back)) : bool));

Range stripLeft(Range, E)(Range*range*, E*element*) if (isInputRange!Range && is(typeof(*range*.front ==*element*) : bool));

Range stripLeft(alias pred, Range)(Range*range*) if (isInputRange!Range && is(typeof(pred(*range*.front)) : bool));

Range stripRight(Range, E)(Range*range*, E*element*) if (isBidirectionalRange!Range && is(typeof(*range*.back ==*element*) : bool));

Range stripRight(alias pred, Range)(Range*range*) if (isBidirectionalRange!Range && is(typeof(pred(*range*.back)) : bool)); - The strip group of functions allow stripping of either leading, trailing, or both leading and trailing elements.The stripLeft function will strip the front of the
*range*, the stripRight function will strip the back of the*range*, while the strip function will strip both the front and back of the*range*. Note that the strip and stripRight functions require the*range*to be a BidirectionalRange*range*. All of these functions come in two varieties: one takes a target*element*, where the*range*will be stripped as long as this*element*can be found. The other takes a lambda predicate, where the*range*will be stripped as long as the predicate returns**true**.Examples:Strip leading and trailing elements equal to the target*element*.assert(" foobar ".strip(' ') == "foobar"); assert("00223.444500".strip('0') == "223.4445"); assert("ëëêéüŗōpéêëë".strip('ë') == "êéüŗōpéê"); assert([1, 1, 0, 1, 1].strip(1) == [0]); assert([0.0, 0.01, 0.01, 0.0].strip(0).length == 2);

Examples:Strip leading and trailing elements while the predicate returns**true**.assert(" foobar ".strip!(a => a == ' ')() == "foobar"); assert("00223.444500".strip!(a => a == '0')() == "223.4445"); assert("ëëêéüŗōpéêëë".strip!(a => a == 'ë')() == "êéüŗōpéê"); assert([1, 1, 0, 1, 1].strip!(a => a == 1)() == [0]); assert([0.0, 0.01, 0.5, 0.6, 0.01, 0.0].strip!(a => a < 0.4)().length == 2);

Examples:Strip leading elements equal to the target*element*.assert(" foobar ".stripLeft(' ') == "foobar "); assert("00223.444500".stripLeft('0') == "223.444500"); assert("ůůűniçodêéé".stripLeft('ů') == "űniçodêéé"); assert([1, 1, 0, 1, 1].stripLeft(1) == [0, 1, 1]); assert([0.0, 0.01, 0.01, 0.0].stripLeft(0).length == 3);

Examples:Strip leading elements while the predicate returns**true**.assert(" foobar ".stripLeft!(a => a == ' ')() == "foobar "); assert("00223.444500".stripLeft!(a => a == '0')() == "223.444500"); assert("ůůűniçodêéé".stripLeft!(a => a == 'ů')() == "űniçodêéé"); assert([1, 1, 0, 1, 1].stripLeft!(a => a == 1)() == [0, 1, 1]); assert([0.0, 0.01, 0.10, 0.5, 0.6].stripLeft!(a => a < 0.4)().length == 2);

Examples:Strip trailing elements equal to the target*element*.assert(" foobar ".stripRight(' ') == " foobar"); assert("00223.444500".stripRight('0') == "00223.4445"); assert("ùniçodêéé".stripRight('é') == "ùniçodê"); assert([1, 1, 0, 1, 1].stripRight(1) == [1, 1, 0]); assert([0.0, 0.01, 0.01, 0.0].stripRight(0).length == 3);

Examples:Strip trailing elements while the predicate returns**true**.assert(" foobar ".stripRight!(a => a == ' ')() == " foobar"); assert("00223.444500".stripRight!(a => a == '0')() == "00223.4445"); assert("ùniçodêéé".stripRight!(a => a == 'é')() == "ùniçodê"); assert([1, 1, 0, 1, 1].stripRight!(a => a == 1)() == [1, 1, 0]); assert([0.0, 0.01, 0.10, 0.5, 0.6].stripRight!(a => a > 0.4)().length == 3);

- pure nothrow @nogc @trusted void swap(T)(ref T
*lhs*, ref T*rhs*) if (isBlitAssignable!T && !is(typeof(*lhs*.proxySwap(*rhs*)))); - Swaps
*lhs*and*rhs*. The instances*lhs*and*rhs*are moved in memory, without ever calling opAssign, nor any other function. T need not be assignable at all to be swapped.If*lhs*and*rhs*reference the same instance, then nothing is done.*lhs*and*rhs*must be mutable. If T is a struct or union, then its fields must also all be (recursively) mutable.Parameters:T *lhs*Data to be swapped with *rhs*.T *rhs*Data to be swapped with *lhs*.Examples:// Swapping POD (plain old data) types: int a = 42, b = 34; swap(a, b); assert(a == 34 && b == 42); // Swapping structs with indirection: static struct S { int x; char c; int[] y; } S s1 = { 0, 'z', [ 1, 2 ] }; S s2 = { 42, 'a', [ 4, 6 ] }; swap(s1, s2); assert(s1.x == 42); assert(s1.c == 'a'); assert(s1.y == [ 4, 6 ]); assert(s2.x == 0); assert(s2.c == 'z'); assert(s2.y == [ 1, 2 ]); // Immutables cannot be swapped: immutable int imm1, imm2; static assert(!__traits(compiles, swap(imm1, imm2)));

Examples:// Non-copyable types can still be swapped. static struct NoCopy { this(this) { assert(0); } int n; string s; } NoCopy nc1, nc2; nc1.n = 127; nc1.s = "abc"; nc2.n = 513; nc2.s = "uvwxyz"; swap(nc1, nc2); assert(nc1.n == 513 && nc1.s == "uvwxyz"); assert(nc2.n == 127 && nc2.s == "abc"); swap(nc1, nc1); swap(nc2, nc2); assert(nc1.n == 513 && nc1.s == "uvwxyz"); assert(nc2.n == 127 && nc2.s == "abc"); // Types containing non-copyable fields can also be swapped. static struct NoCopyHolder { NoCopy noCopy; } NoCopyHolder h1, h2; h1.noCopy.n = 31; h1.noCopy.s = "abc"; h2.noCopy.n = 65; h2.noCopy.s = null; swap(h1, h2); assert(h1.noCopy.n == 65 && h1.noCopy.s == null); assert(h2.noCopy.n == 31 && h2.noCopy.s == "abc"); swap(h1, h1); swap(h2, h2); assert(h1.noCopy.n == 65 && h1.noCopy.s == null); assert(h2.noCopy.n == 31 && h2.noCopy.s == "abc"); // Const types cannot be swapped. const NoCopy const1, const2; static assert(!__traits(compiles, swap(const1, const2)));

- Tuple!(Range1, Range2) swapRanges(Range1, Range2)(Range1
*r1*, Range2*r2*) if (isInputRange!Range1 && isInputRange!Range2 && hasSwappableElements!Range1 && hasSwappableElements!Range2 && is(ElementType!Range1 == ElementType!Range2)); - Swaps all elements of
*r1*with successive elements in*r2*. Returns a tuple containing the remainder portions of*r1*and*r2*that were not swapped (one of them will be empty). The ranges may be of different types but must have the same element type and support swapping.Examples:int[] a = [ 100, 101, 102, 103 ]; int[] b = [ 0, 1, 2, 3 ]; auto c = swapRanges(a[1 .. 3], b[2 .. 4]); assert(c[0].empty && c[1].empty); assert(a == [ 100, 2, 3, 103 ]); assert(b == [ 0, 1, 101, 102 ]);

- void uninitializedFill(Range, Value)(Range
*range*, Value*value*) if (isInputRange!Range && hasLvalueElements!Range && is(typeof(*range*.front =*value*))); - Initializes each element of
*range*with*value*. Assumes that the elements of the*range*are uninitialized. This is of interest for structs that define copy constructors (for all other types, fill and uninitializedFill are equivalent).Parameters:Range *range*An input range that exposes references to its elements and has assignable elements Value *value*Assigned to each element of *range*See Also:Example:

struct S { ... } S[] s = (cast(S*) malloc(5 * S.sizeof))[0 .. 5]; uninitializedFill(s, 42); assert(s == [ 42, 42, 42, 42, 42 ]);