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Function `std.range.chooseAmong`

Choose one of multiple ranges at runtime.


						
				auto chooseAmong(Ranges...)
				(
				

				  size_t index,
				

				  scope return Ranges rs
				

				)
				

				if (Ranges.length >= 2 && allSatisfy!(isInputRange, staticMap!(Unqual, Ranges)) && !is(CommonType!(staticMap!(ElementType, Ranges)) == void));

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.

Parameters

Name	Description
index	which range to choose, must be less than the number of ranges
rs	two or more ranges

Returns

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

Example

auto test()
{
    import std.algorithm.comparison : equal;

    int[4] sarr1 = [1, 2, 3, 4];
    int[2] sarr2 = [5, 6];
    int[1] sarr3 = [7];
    auto arr1 = sarr1[];
    auto arr2 = sarr2[];
    auto arr3 = sarr3[];

    {
        auto s = chooseAmong(0, arr1, arr2, arr3);
        auto t = s.save;
        writeln(s.length); // 4
        writeln(s[2]); // 3
        s.popFront();
        assert(equal(t, only(1, 2, 3, 4)));
    }
    {
        auto s = chooseAmong(1, arr1, arr2, arr3);
        writeln(s.length); // 2
        s.front = 8;
        assert(equal(s, only(8, 6)));
    }
    {
        auto s = chooseAmong(1, arr1, arr2, arr3);
        writeln(s.length); // 2
        s[1] = 9;
        assert(equal(s, only(8, 9)));
    }
    {
        auto s = chooseAmong(1, arr2, arr1, arr3)[1 .. 3];
        writeln(s.length); // 2
        assert(equal(s, only(2, 3)));
    }
    {
        auto s = chooseAmong(0, arr1, arr2, arr3);
        writeln(s.length); // 4
        writeln(s.back); // 4
        s.popBack();
        s.back = 5;
        assert(equal(s, only(1, 2, 5)));
        s.back = 3;
        assert(equal(s, only(1, 2, 3)));
    }
    {
        uint[5] foo = [1, 2, 3, 4, 5];
        uint[5] bar = [6, 7, 8, 9, 10];
        auto c = chooseAmong(1, foo[], bar[]);
        writeln(c[3]); // 9
        c[3] = 42;
        writeln(c[3]); // 42
        writeln(c.moveFront()); // 6
        writeln(c.moveBack()); // 10
        writeln(c.moveAt(4)); // 10
    }
    {
        import std.range : cycle;
        auto s = chooseAmong(0, cycle(arr2), cycle(arr3));
        assert(isInfinite!(typeof(s)));
        assert(!s.empty);
        writeln(s[100]); // 8
        writeln(s[101]); // 9
        assert(s[0 .. 3].equal(only(8, 9, 8)));
    }
    return 0;
}
// works at runtime
auto a = test();
// and at compile time
static b = test();

Authors

Andrei Alexandrescu, David Simcha, Jonathan M Davis, and Jack Stouffer. Credit for some of the ideas in building this module goes to Leonardo Maffi.

License

Boost License 1.0.