tail const

[Andrei Alexandrescu]

On 12/2/10 6:54 PM, Simen kjaeraas wrote:
> Michel Fortin <michel.fortin at michelf.com> wrote:
>
>> I'm not sure I get the problem. Can you show me in code?
>
> const a = map!"a+a"( [1,2,3] );
>
> foreach ( e; a ) {
> }
>
> The foreach fails because popFront is not const. What is needed is for
> typeof(a) to be Map!("a+a", const(int)[]). IOW,
> is( const(Map!("a+a", int[])) == Map!("a+a", const(int)[]) ).
>
> One possible way to do this is for all types T to have defined types
> immutable_t and const_t, which by default alias to immutable(T) and
> const(T), but can be defined to alias to other types. The compiler
> would then automagically convert cast(const)T to cast(T.const_t)T.

Well the code asks for a constant object, and I don't see it as 
reasonable for the type system to automagically infer the intent. What 
should work is this:

const(int)[] data = [1,2,3];
auto a = map!"a+a"(data);
foreach (e;a) {
}

Andrei