tail const

[Steven Schveighoffer]

On Thu, 02 Dec 2010 22:17:53 -0500, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> 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) {
> }

Now, change data to an SList range.  This is what I'm talking about.   
Arrays already enjoy the benefits of tail-const, I want to extend that to  
all range types (and in fact all struct types).

-Steve