D almost has concepts (lite)

[TommiT]

On Friday, 29 March 2013 at 07:52:13 UTC, deadalnix wrote:
> On Friday, 29 March 2013 at 07:48:39 UTC, TommiT wrote:
>> TDPL says:
>>
>> "D defines a simple partial ordering relation for functions: 
>> if foo1 can be called with the parameter types of foo2, then 
>> foo1 ≤ foo2."
>>
>> If you made the slightest change in the wording, you'd 
>> basically get the current C++ concepts-lite proposal in D:
>>
>> "D defines a simple partial ordering relation for functions: 
>> if foo1 can be called with all the possible arguments that 
>> foo2 can be called with, then foo1 ≤ foo2."
>>
>> At first, it almost sounds like the same statement, but now 
>> this would compile:
>>
>> void fun(T)(T) if (T.sizeof >= 2) { }
>> void fun(T)(T) if (T.sizeof >= 4) { }
>>
>> void main()
>> {
>>    fun(42); //calls the second one
>> }
>>
>> I don't know if D would be better like that, but I just wanted 
>> point out how close the spec is to saying that.
>
> That sound unimplementable, sorry.

I think we have different interpretations of what it means when 
function is callable. I think that foo is callable with int 
argument:

void foo(T)(T x)
{
     x("asdf");
}

void main()
{
     int n;
     foo(n); // the function call is made
}

It's just that there's a bug in foo's implementation that fails 
to compile, but the call to foo is yet made, i.e. foo is callable 
with an int argument.