Re: [boost] [function types] New tag type logic

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2005-06-30 06:49:29

John Maddock wrote:
>>OK, here is my current top-candidate:
>>
>>   When classifying types it is often necessary to match against
>>   several variations of one aspect.
>>
>>   There are special variations which make this possible. These are called
>>   *abstract*.
>>
>>   The most important case is to match any variation; that is, to ignore
>>   that aspect in the context of type classification. Because of this, 
>>every
>>aspect has at
>>   least one abstract variation named "unspecified_" plus the aspect name.
> 

;-( - I knew this would happen... I accidently hit the "Send"-button before the 
post was finished...

> 
> That one also makes sense to me, I'm still not sure that "abstract" is the 
> right word though :-)
> 
> Explanation: to me if something is "abstract" then you need to add something 
> to it, extend it in some way to make it concrete.  What you're doing is 

Interesting... This is exactly why I came up with this term in the first place:

An abstract variation of an aspect does not concretely describe the aspect
of the kind of type. It describes it, well, in an /abstract/ way:

Looking at classification, analog to pointer declaration, we constrain a (kind of) 
type by specifying a special (kind of) type that only describes a category (but 
nothing concrete).

Type synthesis is in some ways similar to a constructor call: actually we can't 
create an "unspecified decorated" function type - we can only create an 
undecorated or (member-)pointer-decorated or reference-decorated function type. So 
there /is/ the kind of extension you describe, although implicitly done by a 
default mechanism.

"Abstract" let's the user intuitively suspect something like an "external tree 
structure" (i.e. only leafes carry user data), that's why I like it.

> combining several concrete definitions to form a non-specific union of some 
> kind.  So a quick trip to thesaurus.com suggests: "composite", "compound" or 
> "mixed" as possible names, do any of these work for you?
> 

I'm not convinced, yet. Maybe I'm having difficulties to fully understand you. Can 
you perhaps try to clarify what makes "abstract" unsuitable in your opinion?

Thanks,

Tobias