Proposal: Static Invariant (C++ concept in D)

[Robert Fraser]

davidl Wrote:

> I've read a little bit stuff of C++ concept, and find it has some  
> similarity with
> D's runtime invariant in some abstraction. In some extent , we can imagine  
> C++
> concept is kind of compile time invariant.
> 
> So the following:
> 
> class TemplateClass(T)
> {
>    static invariant()   // reuse keywords, nothing more get introduced
>    {
>      // prerequisite checking, does T have foo , does T have bar
>      Base_Concept_check();  // these emulate the inheritance of concept
>      Derived_Concept_check();
>    }
> }
> 
> Thanks for the great discussion & help from h3r3tic, LeoD, Alexander,  
> Larsivi
> They gave me some comments, and ideas.
> 
> Though it might not functionate all possiblities of C++ concept , but it  
> brings
> us a little bit more powerful way to make sure our templates go all fine.  
> Hope
> people love this idea :D
> 
> 
> DavidL

Isn't this what a static assert is? If you want sets of static assertions, you can always use template mixins.

template LionAssertions()
{
    static assert(Lion.foodChainPosition == FoodChain.max);
    static assert(Mufasa > Aslan, "this program contains evil lies");
}

class Lion : AwesomenessIncarnate
{
    mixin LionAssertions!()
}