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Module std.algorithm.iteration

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

Cheat Sheet
Function Name Description
cache Eagerly evaluates and caches another range's front.
cacheBidirectional As above, but also provides back and popBack.
chunkBy chunkBy!((a,b) => a[1] == b[1])([[1, 1], [1, 2], [2, 2], [2, 1]]) returns a range containing 3 subranges: the first with just [1, 1]; the second with the elements [1, 2] and [2, 2]; and the third with just [2, 1].
cumulativeFold cumulativeFold!((a, b) => a + b)([1, 2, 3, 4]) returns a lazily-evaluated range containing the successive reduced values 1, 3, 6, 10.
each each!writeln([1, 2, 3]) eagerly prints the numbers 1, 2 and 3 on their own lines.
filter filter!(a => a > 0)([1, -1, 2, 0, -3]) iterates over elements 1 and 2.
filterBidirectional Similar to filter, but also provides back and popBack at a small increase in cost.
fold fold!((a, b) => a + b)([1, 2, 3, 4]) returns 10.
group group([5, 2, 2, 3, 3]) returns a range containing the tuples tuple(5, 1), tuple(2, 2), and tuple(3, 2).
joiner joiner(["hello", "world!"], "; ") returns a range that iterates over the characters "hello; world!". No new string is created - the existing inputs are iterated.
map map!(a => a * 2)([1, 2, 3]) lazily returns a range with the numbers 2, 4, 6.
permutations Lazily computes all permutations using Heap's algorithm.
reduce reduce!((a, b) => a + b)([1, 2, 3, 4]) returns 10. This is the old implementation of fold.
splitter Lazily splits a range by a separator.
sum Same as fold, but specialized for accurate summation.
uniq Iterates over the unique elements in a range, which is assumed sorted.

Functions

Name Description
cache cache eagerly evaluates front of range on each construction or call to popFront, to store the result in a cache. The result is then directly returned when front is called, rather than re-evaluated.
cacheBidirectional cache eagerly evaluates front of range on each construction or call to popFront, to store the result in a cache. The result is then directly returned when front is called, rather than re-evaluated.
chunkBy Chunks an input range into subranges of equivalent adjacent elements. In other languages this is often called partitionBy, groupBy or sliceWhen.
group Groups consecutively equivalent elements into a single tuple of the element and the number of its repetitions.
joiner Lazily joins a range of ranges with a separator. The separator itself is a range. If a separator is not provided, then the ranges are joined directly without anything in between them (often called flatten in other languages).
permutations Lazily computes all permutations of r using Heap's algorithm.
splitter Lazily splits a range using an element as a separator. This can be used with any narrow string type or sliceable range type, but is most popular with string types.
splitter Similar to the previous overload of splitter, except this one uses another range as a separator. This can be used with any narrow string type or sliceable range type, but is most popular with string types. The predicate is passed to std.functional.binaryFun, and can either accept a string, or any callable that can be executed via pred(r.front, s.front).
splitter Similar to the previous overload of splitter, except this one does not use a separator. Instead, the predicate is an unary function on the input range's element type. The isTerminator predicate is passed to std.functional.unaryFun and can either accept a string, or any callable that can be executed via pred(element, s).
splitter Lazily splits the string s into words, using whitespace as the delimiter.
sum Sums elements of r, which must be a finite input range. Although conceptually sum(r) is equivalent to fold!((a, b) => a + b)(r, 0), sum uses specialized algorithms to maximize accuracy, as follows.
uniq Lazily iterates unique consecutive elements of the given range (functionality akin to the uniq system utility). Equivalence of elements is assessed by using the predicate pred, by default "a == b". The predicate is passed to std.functional.binaryFun, and can either accept a string, or any callable that can be executed via pred(element, element). If the given range is bidirectional, uniq also yields a bidirectional range.

Structs

Name Description
Group Groups consecutively equivalent elements into a single tuple of the element and the number of its repetitions.
Permutations Lazily computes all permutations of r using Heap's algorithm.

Templates

Name Description
cumulativeFold Similar to fold, but returns a range containing the successive reduced values. The call cumulativeFold!(fun)(range, seed) first assigns seed to an internal variable result, also called the accumulator. The returned range contains the values result = fun(result, x) lazily evaluated for each element x in range. Finally, the last element has the same value as fold!(fun)(seed, range). The one-argument version cumulativeFold!(fun)(range) works similarly, but it returns the first element unchanged and uses it as seed for the next elements. This function is also known as partial_sum, accumulate, scan, Cumulative Sum.
each Eagerly iterates over r and calls pred over each element.
filter auto filter(Range)(Range rs) if (isInputRange!(Unqual!Range));
filterBidirectional auto filterBidirectional(Range)(Range r) if (isBidirectionalRange!(Unqual!Range));
fold Implements the homonym function (also known as accumulate, compress, inject, or foldl) present in various programming languages of functional flavor. The call fold!(fun)(range, seed) first assigns seed to an internal variable result, also called the accumulator. Then, for each element x in range, result = fun(result, x) gets evaluated. Finally, result is returned. The one-argument version fold!(fun)(range) works similarly, but it uses the first element of the range as the seed (the range must be non-empty).
map auto map(Range)(Range r) if (isInputRange!(Unqual!Range));
reduce Implements the homonym function (also known as accumulate, compress, inject, or foldl) present in various programming languages of functional flavor. There is also fold which does the same thing but with the opposite parameter order. The call reduce!(fun)(seed, range) first assigns seed to an internal variable result, also called the accumulator. Then, for each element x in range, result = fun(result, x) gets evaluated. Finally, result is returned. The one-argument version reduce!(fun)(range) works similarly, but it uses the first element of the range as the seed (the range must be non-empty).

Authors

Andrei Alexandrescu

License

Boost License 1.0.

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