Why doesn't this work in D2?

[Philippe Sigaud]

On Mon, Jun 28, 2010 at 10:56, Jacob Carlborg <doob at me.com> wrote:

Something to keep in mind: as of 2.04x (.045? maybe), the way UTF-8 / UTF-32
is managed was changed. "asd" is an array of immutable(dchar), not
imutable(char). At least DMD tells me that its element type is 'dchar'.

So your function can be done this way in D2:

void foo(T,U)(in T[] a, U b) if (is(U : Unqual!T)) // that compiles only if
b can be cast to A
{
    writeln(a,b);
}

"asd".foo('s'); // prints "asds".

is(U == Unqual!T) does not work, for U is 'char' while Unqual!T is 'dchar'.

More generally, using ranges and not arrays, the template becomes a bit more
heavy:

void foo(Range,Elem)(in Range range, Elem elem)
if (isInputRange!Range && is(Elem : Unqual!(ElementType!Range)))
{
...
}


I don't think I understand what you're showing here. How would I strip off
> the const/immutable with a template ?
>
>
Hmmm...
* plays with is expressions *

This seems to work:

template UnConst(T)
{
    static if (is(T t == const U, U)) // that is:  'if T is a 'const U', for
some U'
        alias U UnConst;                      // then give me the U, (ie, T
without a const)
    else
        alias T UnConst;                      // else give me the (original)
T
}

template UnImmutable(T)
{
    static if (is(T t == immutable U, U)) // 'if T is an 'immutable U', for
some U'
        alias U UnImmutable;
    else
        alias T UnImmutable;
}

test:

void main() {
    alias const int Int;
    writeln(UnConst!Int.stringof);
    writeln(Int.stringof);
    writeln(UnConst!int.stringof);
    writeln(UnConst!(const int).stringof);
    writeln(UnConst!(immutable int).stringof);

    alias immutable int IInt;
    writeln(UnConst!IInt.stringof);
    writeln(IInt.stringof);
    writeln(UnImmutable!int.stringof);
    writeln(UnImmutable!(const int).stringof);
    writeln(UnImmutable!(immutable int).stringof);
}

Philippe
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