Fallback 'catch-all' template functions

[Xinok via Digitalmars-d]

On Thursday, 1 September 2016 at 05:37:50 UTC, Manu wrote:
> So, consider a set of overloads:
>
>   void f(T)(T t) if(isSomething!T) {}
>   void f(T)(T t) if(isSomethingElse!T) {}
>   void f(T)(T t) {}
>
> I have a recurring problem where I need a fallback function 
> like the bottom one, which should be used in lieu of a more 
> precise match. This is obviously an ambiguous call, but this is 
> a pattern that comes up an awful lot. How to do it in D?
>
> I've asked this before, and people say:
>
>   void f(T)(T t) if(!isSomething!T && !isSomethingElse!T) {}
>
> Consider that more overloads are being introduced by users 
> spread out across many modules that define their own kind of T; 
> this solution is no good.

In the past, I have suggested using the "default" keyword to 
specify a fallback function of this kind. I think it's a useful 
pattern for generic algorithms that have optimized variants on 
specific types for performance.

    void f(T)(T t) if(isSomething!T) {}
    void f(T)(T t) if(isSomethingElse!T) {}
    void f(T)(T t) default {}