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Template std.algorithm.iteration.each

Eagerly iterates over r and calls fun over each element.

template each(alias fun) ;

If no function to call is specified, each defaults to doing nothing but consuming the entire range. r.front will be evaluated, but that can be avoided by specifying a lambda with a lazy parameter.

each also supports opApply-based types, so it works with e.g. parallel.

Normally the entire range is iterated. If partial iteration (early stopping) is desired, fun needs to return a value of type Flag!"each" (Yes.each to continue iteration, or No.each to stop iteration).

Contained Functions

NameDescription
each

Parameters

NameDescription
fun function to apply to each element of the range
r range or iterable over which each iterates

Returns

Yes.each if the entire range was iterated, No.each in case of early stopping.

See Also

std.range.tee

Example

import std.range : iota;
import std.typecons : Flag, Yes, No;

long[] arr;
iota(5).each!(n => arr ~= n);
writeln(arr); // [0, 1, 2, 3, 4]
iota(5).each!((n) { arr ~= n; return No.each; });
writeln(arr); // [0, 1, 2, 3, 4, 0]

// If the range supports it, the value can be mutated in place
arr.each!((ref n) => n++);
writeln(arr); // [1, 2, 3, 4, 5, 1]

arr.each!"a++";
writeln(arr); // [2, 3, 4, 5, 6, 2]

// by-ref lambdas are not allowed for non-ref ranges
static assert(!is(typeof(arr.map!(n => n).each!((ref n) => n++))));

// The default predicate consumes the range
auto m = arr.map!(n => n);
(&m).each();
assert(m.empty);

// Indexes are also available for in-place mutations
arr[] = 0;
arr.each!"a=i"();
writeln(arr); // [0, 1, 2, 3, 4, 5]

// opApply iterators work as well
static class S
{
    int x;
    int opApply(scope int delegate(ref int _x) dg) { return dg(x); }
}

auto s = new S;
s.each!"a++";
writeln(s.x); // 1

Example

each works with iterable objects which provide an index variable, along with each element 

import std.range : iota, lockstep;

auto arr = [1, 2, 3, 4];

// 1 ref parameter
arr.each!((ref e) => e = 0);
writeln(arr.sum); // 0

// 1 ref parameter and index
arr.each!((i, ref e) => e = cast(int) i);
writeln(arr.sum); // 4.iota.sum

Authors

Andrei Alexandrescu

License

Boost License 1.0.