Fun with templates

[TommiT]

On Saturday, 6 July 2013 at 13:30:02 UTC, TommiT wrote:
> Some more details of this proposed feature:
>
> inout(T) foo(inout T)(T a, T b)
> {
>     return var;
> }
>
> void bar(inout T)(T a, T b)
> {
>     a = b;
> }
>
> void main()
> {
>     const int con;
>     immutable int imm;
>
>     foo(con, con); // OK (returns const int)
>     foo(con, imm); // Error: returned inout(T) is ambiguous
>
>     bar(con, con); // OK
>     bar(con, imm); // OK (no ambiguity because inout not used)
> }

Another approach, if we wanted a different syntax, would be to 
add a new keyword 'mutable'. Like immutable overrides const, 
mutable would override both const and immutable:

static assert(is(mutable(const(int)) == int));
static assert(is(mutable(immutable(int)) == int));

Here's how it would look:

T foo(T)(mutable(T) a, mutable(T) b)
{
     a = b = 123;
     return a;
}

void main()
{
     const int con;
     immutable int imm;

     foo(con, con); // OK (returns const int)
     foo(con, imm); // Error: T is ambiguous
}