why can't structs implement interfaces?

[wakko]

Saaa a écrit :
> struct S : Pos {}
> Why is this not possible? 
> 

It's not and structures have no vtable... fortunately.

But, could it be a good idea to use the "inheritance operator" to do 
some kind of static inheritance like we do with mixins or to force 
implementation at compile-time ?


1. inheriting from an interfaces would force function implementation at 
compile time:

interface IFoo
{
	void foo();
}

// Would not compile
// "Struct S static interface function IFoo.foo isn't implemented"
struct S : IFoo {}

// Would compile
struct S : IFoo { void foo() {} }


2. inheriting from a structure would do some kind a mixin.

struct S1 { void foo(); static void bar(); }
struct S2 : S1 {}
S1.bar();
S1 a; a.foo(); a.bar();


3. class and structs could share interfaces for compile time function 
name resolution. I think this already work using untyped template arguments.

interface IFoo
{
	void foo();
}

class C : IFoo // dynamic inheritance
{
	void foo()
	{
	}
}

struct S : IFoo // static inheritance
{
	void foo()
	{
	}
}

class Bar(IFoo FOO)
{
	void bar(FOO thing)
	{
		thing.foo();
	}
}


4. casting could be forbidden OR :

struct A { int a; }
struct B : A {} // B implements "int a" as in 2

A a; B b = a; // would do something like b.a = a.a
B b; A a = b; // would do something like a.a = b.a


--
AF