auto concat(T : E[n], E, size_t n)(const 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;
}
static immutable ubyte[4] sigma0 = [101, 120, 112, 97];
static immutable ubyte[4] sigma1 = [110, 100, 32, 51];
static immutable ubyte[4] sigma2 = [ 50, 45, 98, 121];
static immutable ubyte[4] sigma3 = [116, 101, 32, 107];
void func(in ref ubyte[32] key, in ref ubyte[16] n) @nogc
{
ubyte[64] buf;
buf[0..4] = sigma0;
buf[4..20] = key[0..16];
buf[20..24] = sigma1;
buf[24..40] = n;
buf[40..44] = sigma2;
buf[44..60] = key[16..$];
buf[60..64] = sigma3;
auto buf2 = concat!(ubyte[64])(sigma0, key[0..16], sigma1, n,
sigma2, key[16..$], sigma3);
assert(buf == buf2);
}
void main() {
ubyte[32] key =
[0,1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0,1];
ubyte[16] n = key[0..16];
func(key, n);
}
Some remarks:
* I added `ref` to `func`'s parameters, because the arrays are
relatively large, so passing them by value might be costly (you
should measure it if you care).
* The `void` initialization in `concat` is an optimization that
is valid only for POD types.
* Returning the array is cheap because of NRVO.
