Function std.range.chooseAmong

The ranges may be different, but they must have compatible element types. The result is a range that offers the weakest capabilities of all Ranges.

Prototype

auto chooseAmong(Ranges...)(
  size_t index,
  Ranges rs
)
if (Ranges.length > 2 && is(typeof(choose(true, rs[0], rs[1]))) && is(typeof(chooseAmong(0, rs[1..__dollar]))));

Parameters

Returns

The indexed range. If rs consists of only one range, the return type is an alias of that range's type.

Example

import std.algorithm : equal;

int[] arr1 = [ 1, 2, 3, 4 ];
int[] arr2 = [ 5, 6 ];
int[] arr3 = [ 7 ];

{
    auto s = chooseAmong(0, arr1, arr2, arr3);
    auto t = s.save;
    assert(s.length == 4);
    assert(s[2] == 3);
    s.popFront();
    assert(equal(t, [1, 2, 3, 4][]));
}
{
    auto s = chooseAmong(1, arr1, arr2, arr3);
    assert(s.length == 2);
    s.front = 8;
    assert(equal(s, [8, 6][]));
}
{
    auto s = chooseAmong(1, arr1, arr2, arr3);
    assert(s.length == 2);
    s[1] = 9;
    assert(equal(s, [8, 9][]));
}
{
    auto s = chooseAmong(1, arr2, arr1, arr3)[1..3];
    assert(s.length == 2);
    assert(equal(s, [2, 3][]));
}
{
    auto s = chooseAmong(0, arr1, arr2, arr3);
    assert(s.length == 4);
    assert(s.back == 4);
    s.popBack();
    s.back = 5;
    assert(equal(s, [1, 2, 5][]));
    s.back = 3;
    assert(equal(s, [1, 2, 3][]));
}
{
    uint[] foo = [1,2,3,4,5];
    uint[] bar = [6,7,8,9,10];
    auto c = chooseAmong(1,foo, bar);
    assert(c[3] == 9);
    c[3] = 42;
    assert(c[3] == 42);
    assert(c.moveFront() == 6);
    assert(c.moveBack() == 10);
    assert(c.moveAt(4) == 10);
}
{
    import std.range : cycle;
    auto s = chooseAmong(1, cycle(arr2), cycle(arr3));
    assert(isInfinite!(typeof(s)));
    assert(!s.empty);
    assert(s[100] == 7);
}