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

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2005-06-30 08:24:58

David Abrahams wrote:
> Tobias Schwinger <tschwinger_at_[hidden]> writes:
> 
> 
>>I don't believe it's metaprogramming specific -- let's clear up the logic, first:
>>
>>
>>>it is unclear to me whether
>>>the common case is "ignoring an aspect" or if it is really "allowing a
>>>match for any variation of an aspect" 
>>
>>Given a variable 'a' which can be either '1', '2' or '3' it doesn't make a difference:
>>
>>    if ((a == 1) || (a == 2) || (a == 3)) // match any variation of a
>>    {
>>      // do something
>>    }
>>
>>is logically equivalent to
>>
>>    // no if -- just ignore a
>>    {
>>      // do something
>>    }
>>
>>
>>>which I can do by "ignoring an
>>>aspect."
>>>
>>
>>Equivalence is commutative:
>>
>>You can ignore 'a' by allowing any variation and you can allow any variation by 
>>ignoring 'a' -- no difference, again.
>>
>>Making any difference would be talking about implementation details in a parapraph 
>>about plain logic.
> 
> 
> Isn't this a complicated way of saying something simple?  Is it

It undoubtfully is ;-). And awfully over-formalized. It's clear, though.

> important or useful to point out that doing "something"
> unconditionally is a special case of doing "something" only for
> certain values of "a?"
> 

It generally isn't. However, I believe it makes some sense to menion the case in 
the particular case of the paragraph we are discussing here. To try the section 
back-merged into the text see:

     http://lists.boost.org/boost/2005/06/29469.php

Thanks,

Tobias