On 03/11/2012 10:48 AM, Nick Sabalausky wrote:
Maybe it's just half-asleep crazy-talk, but you know what I think would be
great in Phobos (I don't *think* it's already there)? A virtual-like
"dispatch" function, which would help ease the rift between template code
and OOP. For example, if you have a class hierarchy, you can do
single-dispatch via method overriding. But if you have a function implemeted
outside the class that uses overloading on type, you have to dispatch
manually:
class FooBase {}
class Foo1 : FooBase {}
class Foo2 : FooBase {}
class Foo3 : FooBase {}
void bar(FooBase f)
{
if(auto _f = cast(Foo1)f)
bar(_f);
else if(auto _f = cast(Foo1)f)
bar(_f);
else if(auto _f = cast(Foo2)f)
bar(_f);
else
throw new Exception("Can't dispatch");
}
void bar(T f) if(is(T : FooBase))
{
// use 'f'
}
Thats a lot of boilerplate!
I'm finding I need to do that sort of thing a lot when using my Goldie lib.
It could be improved with a foreach over a TypeTuple, but it'd be great to
have a "dispatch!()()" or even a multiple dispatch version to just automate
all of that entirely. That would grant D the feature of multidispatch and
non-OOP dispatch *in library*, and really help ease the rift between OOP and
non-OOP styles of coding.
Or, the same thing but without a class hierarchy. For example, if you have
ten different ForwardRange types you want to deal with.
My half-asleep self thinks that that *should* probably be possible to
create.
Yes, it is.
The real trick I think would be in figuring out the
interface/
A overloadSet(A a){ ... }
B overloadSet(B b){ ... }
C overloadSet(B b, C c){ ... }
...
auto dispatch!overloadSet(args...)
The return type would just be the common type of all overload set return
types.
semantics
The main issue is how to deal with ambiguities and non-existence of a
suitable method.
for controlling what types to actually try to dispatch on.
