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Implements the homonym function (also known as transform) present in many languages of functional flavor. The call map!(fun)(range) returns a range of which elements are obtained by applying fun(a) left to right for all elements a in range. The original ranges are not changed. Evaluation is done lazily.

template map(fun...) ;

Contained Functions



fun one or more transformation functions

See Also

Map (higher-order function)


import std.algorithm.comparison : equal;
import std.range : chain, only;
auto squares =
    chain(only(1, 2, 3, 4), only(5, 6)).map!(a => a * a);
assert(equal(squares, only(1, 4, 9, 16, 25, 36)));


Multiple functions can be passed to map. In that case, the element type of map is a tuple containing one element for each function.

auto sums = [2, 4, 6, 8];
auto products = [1, 4, 9, 16];

size_t i = 0;
foreach (result; [ 1, 2, 3, 4 ].map!("a + a", "a * a"))
    writeln(result[0]); // sums[i]
    writeln(result[1]); // products[i]


You may alias map with some function(s) to a symbol and use it separately:

import std.algorithm.comparison : equal;
import std.conv : to;

alias stringize = map!(to!string);
assert(equal(stringize([ 1, 2, 3, 4 ]), [ "1", "2", "3", "4" ]));


Andrei Alexandrescu


Boost License 1.0.