Slides from my ACCU Silicon Valley talk

[Andrei Alexandrescu]

On 12/14/10 7:33 AM, biozic wrote:
> Le 14/12/10 09:56, Andrei Alexandrescu a écrit :
>> On 12/14/10 2:23 AM, Walter Bright wrote:
>>> bearophile wrote:
>>>> Andrei:
>>>>
>>>>> D's constrained templates were introduced on 17 June 2008 and they've
>>>>> been
>>>>> a smashing hit. Virtually all of Phobos uses them, and I'm sure a
>>>>> lot of
>>>>> generic client code. They take half a minute to explain and solve a
>>>>> difficult problem in a very simple manner.<
>>>>
>>>> A template with two constrains makes it less handy to add error
>>>> messages that
>>>> explain why the instantiation has failed:
>>>
>>> Adding such error messages misses the point of constraints. The idea is
>>> that template overloading is based on constraints. Given 3 templates
>>> with 3 constraints, overload resolution picks the one with constraints
>>> that pass. Giving error messages for the others is wrong.
>>>
>>> If you want it to produce error messages if the instantiation is wrong,
>>> the correct way is to use static asserts within the template body. No
>>> additional features serve any purpose.
>>
>> Yah, I was planning on writing the same response.
>>
>> Andrei
>
> I have a question about this and some pieces of code in the standard
> library, notably std.algorithm: some of the templated functions use
> template constraints even when no template overloading is taking place.
> Wouldn't some static asserts help print more accurate messages when
> these functions are misused?
>
> Nicolas

The intent is to allow other code to define functions such as e.g. "map" 
or "sort". Generally any generic function should exclude via a 
constraint the inputs it can't work on. That way no generic function 
bites off more than it can chew.

Andrei