Re: Initializing static array with contents of (static and dynamic) arrays

[Ali Çehreli via Digitalmars-d-learn]

On 07/04/2016 07:31 AM, Johannes Loher wrote:
> In a project I am currently working on, I have lot's of code of the
> following form:
>
> 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 ubyte[32] key, in ubyte[16] n)
> {
>      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;
>
>     /* do something with buf */
> }
Here's an option that overlays a struct on top of the bytes:

struct Buf {
    union {
        struct {
            ubyte[4] sigma0 = [101, 120, 112,  97];
            ubyte[16] keyBeg;
            ubyte[4] sigma1 = [110, 100,  32,  51];
            ubyte[16] n;
            ubyte[4] sigma2 = [ 50,  45,  98, 121];
            ubyte[16] keyEnd;
            ubyte[4] sigma3 = [116, 101,  32, 107];
        }

        ubyte[64] bytes;
    }

    this(const ubyte[] key, const ubyte[] n) {
        this.keyBeg = key[0..16];
        this.keyEnd = key[16..$];
        this.n = n;
    }
}

static assert(Buf.sizeof == 64);

void func(in ubyte[] key, in ubyte[] n) {
    auto buf = Buf(key, n);
    writeln(buf.bytes);
}

import std.stdio;
import std.range;
import std.array;

void main() {
    func(ubyte(32).iota.array,
         ubyte(16).iota.array);
}

Prints:

[101, 120, 112, 97, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 
15, 110, 100, 32, 51, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 
15, 50, 45, 98, 121, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 
29, 30, 31, 116, 101, 32, 107]

Ali