module utility;

auto concat(T : E[n], E, size_t n)(in E[][] args...) @nogc
{
    size_t offset = 0;
    T result = void;
    foreach(arr; args) {
        result[offset .. offset+arr.length] = arr;
        offset += arr.length;
    }
    assert(offset == result.length);
    return result;
}

@safe unittest
{
    assert(concat!(int[0])() == []);
    assert(concat!(int[0])([]) == []);
    assert(concat!(int[0])([], []) == []);
    assert(concat!(int[1])([1]) == [1]);
    assert(concat!(int[1])([1], []) == [1]);
    assert(concat!(int[1])([], [1]) == [1]);
    assert(concat!(int[2])([1, 2]) == [1, 2]);
    assert(concat!(int[2])([1], [2]) == [1, 2]);
    assert(concat!(int[6])([1], [2, 3], [4, 5, 6]) == [1, 2, 3, 4, 5, 6]);
    assert(concat!(char[12])("Hello", " ", "World!") == "Hello World!");
}