Hello.

I need a template for casting arrays to another type without changing const and immutable attributes:

template ByteType(T) {
  // some magic
}

const(int)[] ca;
immutable(short)[] is;
long[] ml;

static assert(is(ByteType!ca == const(byte)[]));
static assert(is(ByteType!is == immutable(byte)[]));
static assert(is(ByteType!ml == byte[]));

What kind of template magic I should use?

I found awkward solution:

template ByteType(alias t) {
  alias typeof(t) T;
  static if(is(ElementType!T == const)) alias const(byte)[] ByteType;
  else static if(is(ElementType!T == immutable)) alias immutable(byte)[] ByteType;
  else alias byte[] ByteType;
}

Jack Applegame:

> I found awkward solution:
>
> template ByteType(alias t) {
>   alias typeof(t) T;
>   static if(is(ElementType!T == const)) alias const(byte)[] ByteType;
>   else static if(is(ElementType!T == immutable)) alias immutable(byte)[] ByteType;
>   else alias byte[] ByteType;
> }

I think that's essentially the right solution. I suggest to generalize it a bit, removing the byte from its insides, and making it a template argument. I think "shared" is missing.

Bye,
bearophile

On Wednesday, 22 May 2013 at 13:01:26 UTC, bearophile wrote:
> I think that's essentially the right solution. I suggest to generalize it a bit, removing the byte from its insides, and making it a template argument. I think "shared" is missing.
Yes.

Finally http://dpaste.1azy.net/fc503331

Jack Applegame:

> Finally http://dpaste.1azy.net/fc503331

I suggest to use indents composed by 4 spaces.
Generally in D we use template constraints, instead of static ifs with a nice error message...
In such complex situations I also suggest to add braces.

Something like this:


auto castElementType(T = byte, F)(ref F from)
if (isArray!F) {
    alias E = typeof(from[0]);

    static if(is(E == const)) {
        return cast(const(Unqual!T)[])from;
    } else static if(is(E == immutable)) {
        return cast(immutable(Unqual!T)[])from;
    } else static if(is(E == shared)) {
        return cast(shared(Unqual!T)[])from;
    } else {
        return cast(Unqual!T[])from;
    }
}


Bye,
bearophile