I have a tuple of types, I want a template that evaluates to the most specialized base type of all of them. I'll be using it for classes but for other cases it just needs to do something sane (erroring out would do). 

No point in reinventing the wheel so, anyone have such a template laying around?

BCS wrote:

> I have a tuple of types, I want a template that evaluates to the most specialized base type of all of them. I'll be using it for classes but for other cases it just needs to do something sane (erroring out would do).
> 
> No point in reinventing the wheel so, anyone have such a template laying around?

tango.core.Tuple and std.typetuple have templates called MostDerived and DerivedToFront, these might be helpful?

Reply to Lutger,

> BCS wrote:
> 
>> I have a tuple of types, I want a template that evaluates to the most
>> specialized base type of all of them. I'll be using it for classes
>> but for other cases it just needs to do something sane (erroring out
>> would do).
>> 
>> No point in reinventing the wheel so, anyone have such a template
>> laying around?
>> 
> tango.core.Tuple and std.typetuple have templates called MostDerived
> and DerivedToFront, these might be helpful?
>

I might be able to use somthing like that as a starting point but what I want is this

class A {}
class B : A {}
class C : A {}
 class D : C {}
 class E : C {}
class F {}

CCT!(E, D) // == C
CCT!(E, C) // == C
CCT!(E, B) // == A
CCT!(E, A) // == A
CCT!(E, F) // == object

BCS wrote:
> Reply to Lutger,
> 
>> BCS wrote:
>>
>>> I have a tuple of types, I want a template that evaluates to the most
>>> specialized base type of all of them. I'll be using it for classes
>>> but for other cases it just needs to do something sane (erroring out
>>> would do).
>>>
>>> No point in reinventing the wheel so, anyone have such a template
>>> laying around?
>>>
>> tango.core.Tuple and std.typetuple have templates called MostDerived
>> and DerivedToFront, these might be helpful?
>>
> 
> I might be able to use somthing like that as a starting point but what I want is this
> 
> class A {}
> class B : A {}
> class C : A {}
>  class D : C {}
>  class E : C {}
> class F {}
> 
> CCT!(E, D) // == C
> CCT!(E, C) // == C
> CCT!(E, B) // == A
> CCT!(E, A) // == A
> CCT!(E, F) // == object

That sounds like the kind of thing that you're supposed to be able to get from typeof(true?E.init:D.init), but I seem to recall a bug filed by  Andrei the other day saying it doesn't work properly for classes.

--bb

BCS wrote:

> CCT!(E, D) // == C
> CCT!(E, C) // == C
> CCT!(E, B) // == A
> CCT!(E, A) // == A
> CCT!(E, F) // == object

To give it a name:
it's the lowest common ancestor (LCA) in the derivation tree.

-manfred

Reply to Manfred,

> BCS wrote:
> 
>> CCT!(E, D) // == C
>> CCT!(E, C) // == C
>> CCT!(E, B) // == A
>> CCT!(E, A) // == A
>> CCT!(E, F) // == object
> To give it a name:
> it's the lowest common ancestor (LCA) in the derivation tree.
> -manfred
> 

or highest common ancestor (HCL), depending on how you draw your trees.

How about, Closest Common Ancestor (CCL)

with a little insight from #D:

template ExtractClass(T...)
{
	static if(T.length > 0)
	{
		static if(is(T[0] P == class)) alias P ExtractClass;
		else      alias ExtractClass!(T[1..$]) ExtractClass;
	}
	else static assert(false);
}

template BaseClass(T)
{
	static if(is(T _ == class) && !is(_ == Object) && is(T BaseT == super))
		alias ExtractClass!(BaseT) BaseClass;
	else static assert(false);
}

template CCT2(T,U)
{
	static if(is(T _ == class) && is(U __ == class))
	{
		static if (is(T : U))      alias U CCT2;
		else static if (is(U : T)) alias T CCT2;
		else  alias CCT2!(BaseClass!(T),U) CCT2;
	}
	else static assert(false);
}

template CCT(T...)
{
	static if(T.length > 1)       alias CCT!(CCT2!(T[0..2]), T[2..$]) CCT;
	else static if(T.length == 1) alias T[0] CCT;
	else static assert(false);
}


class A {}
class B : A {}
class C : A {}
class D : C {}
class E : C {}
class F {}


static assert(is(CCT!(E, D) == C));
static assert(is(CCT!(E, C) == C));
static assert(is(CCT!(E, B) == A));
static assert(is(CCT!(E, A) == A));
static assert(is(CCT!(E, F) == Object));

rename it as you please <G>

BCS wrote:
> depending on how you draw your trees.

That's also true for 'close'. :-)

-manfred

BCS wrote:

> with a little insight from #D:
[...]

Would you please describe your (hopefully) real world case of usage.

I beg for this, because your algorithm has a worst case lower bound for
the run time of
|   Omega( n * N)
and---if N is fixed---the fastet algorithm has a worst case lower bound
for the runtime of
|   Omega( n + N);
where n is the number of queries to the derivation tree and N is the
number of nodes in the derivation tree.

-manfred