D's type classes pattern ?

matovitch via Digitalmars-d-learn digitalmars-d-learn at puremagic.com
Wed Mar 25 01:16:25 PDT 2015


Thanks for the precisions on template constraint and template
specialization...Indeed wath I want to do look like isInputRange
constraint. Haskell have something like :

//(Pseudo D-Haskell)

void foo(InputRange R)(R r);

//D equivalent

void foo(R)(R r) if (isInputRange(R));

Except they call them type classes instead of template constraint
and it is check at runtime instead of compile time for D.

I am curious to know how isInputRange is implemented since I
wanted to do kind of the same but I am afraid it's full of (ugly)
traits and template trickeries where haskell type classes are
quite neat and essentially a declaration of an interface.

Let say I want to be able to add the type my algo deal with...I
could do an isAddable wich looks if a+b compiles with traits...I
wondered if you could check statically that the type could
implement an interface *if it wanted to* that is, without
inheriting it...





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