Proposal: static template(fail)

[Gregor Richards]

Ary Borenszweig wrote:
> Janice Caron wrote:
>> On 12/13/07, Jason House <jason.james.house at gmail.com> wrote:
>>> Janice Caron Wrote:
>>>
>>>> On 12/13/07, Aziz K. <aziz.kerim at gmail.com> wrote:
>>>>> Why not use a static assert: static assert(0, "Substitution Failure");
>>>> A static assert is a compile error. Different thing. What you want is
>>>> for the template not to be instanted, not for it to be instantiated
>>>> with a compile error.
>>>>
>>>> Put it another way. Suppose you write
>>>>
>>>>     S(int) s;
>>>>
>>>> Which would you prefer - an error message saying that s couldn't be
>>>> instantiated (giving the filename and line number of the above line),
>>>> or an error message saying that a static assert in the middle of some
>>>> library file had been hit?
>>> I'd prefer a static assert.
>>> As with all errors, I'd want a backtrace.
>>
>> You're missing the point, which is IT'S NOT AN ERROR. It's a
>> substitution failure - and substitution failure IS NOT AN ERROR.
>> That's a basic principle of template programming.
> 
> I don't understand how it's not an error if you can't instantiate the 
> template.

Because it could potentially instantiate a different (overloaded) template.

  - Gregor Richards