The OpenD Programming Language

lockstep

Iterate multiple ranges in lockstep using a foreach loop. In contrast to zip it allows reference access to its elements. If only a single range is passed in, the Lockstep aliases itself away. If the ranges are of different lengths and s == StoppingPolicy.shortest stop after the shortest range is empty. If the ranges are of different lengths and s == StoppingPolicy.requireSameLength, throw an exception. s may not be StoppingPolicy.longest, and passing this will throw an exception.

Iterating over Lockstep in reverse and with an index is only possible when s == StoppingPolicy.requireSameLength, in order to preserve indexes. If an attempt is made at iterating in reverse when s == StoppingPolicy.shortest, an exception will be thrown.

By default StoppingPolicy is set to StoppingPolicy.shortest.

Limitations: The pure, @safe, @nogc, or nothrow attributes cannot be inferred for lockstep iteration. zip can infer the first two due to a different implementation.

  1. Lockstep!(Ranges) lockstep(Ranges ranges)
    Lockstep!(Ranges)
    lockstep
    (
    Ranges...
    )
    (
    Ranges ranges
    )
  2. Lockstep!(Ranges) lockstep(Ranges ranges, StoppingPolicy s)

Examples

auto arr1 = [1,2,3,4,5,100];
auto arr2 = [6,7,8,9,10];

foreach (ref a, b; lockstep(arr1, arr2))
{
    a += b;
}

assert(arr1 == [7,9,11,13,15,100]);

/// Lockstep also supports iterating with an index variable:
foreach (index, a, b; lockstep(arr1, arr2))
{
    assert(arr1[index] == a);
    assert(arr2[index] == b);
}

Lockstep also supports iterating with an index variable:

auto arr1 = [0, 1, 2, 3];
auto arr2 = [4, 5, 6, 7];

size_t n = arr1.length -1;
foreach_reverse (index, a, b; lockstep(arr1, arr2, StoppingPolicy.requireSameLength))
{
    assert(n == index);
    assert(index == a);
    assert(arr1[index] == a);
    assert(arr2[index] == b);
    n--;
}

auto arr3 = [4, 5];
n = 1;
foreach_reverse (a, b; lockstep(arr1, arr3))
{
    assert(a == arr1[$-n] && b == arr3[$-n]);
    n++;
}

See Also

zip

lockstep is similar to zip, but zip bundles its elements and returns a range. lockstep also supports reference access. Use zip if you want to pass the result to a range function.

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