Re: [boost] [TypeErasure]

Subject: Re: [boost] [TypeErasure]
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2012-07-23 15:30:26

AMDG

On 07/23/2012 11:17 AM, Markus Werle wrote:
> Steven Watanabe wrote:
> 
>> AMDG
> 
> [*slightly* off-topic: Does that mean Ad maiorem Dei gloriam?]
> 

Yes.

>> On 07/22/2012 07:21 AM, Markus Werle wrote:
>>> Hi Steven!
>>>
>>> I have one question: proto and spirit use _1, _2, etc.
>>> TypeErasure uses _a, _b, _c ...
>>> What was your reason to introduce yet another placeholder set?
>>
> http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/doc/html/boost_typeerasure/design.html#boost_typeerasure.design.placeholder
> 
> I disagree with this decision. You write: 
> 
>> An earlier version of the library used the names _1, _2, etc. 
>> instead of _a, _b, etc. This caused a certain amount of confusion 
>> because the numbered placeholders are already used by several 
>> other libraries including Boost/Std Bind, Boost.Phoenix, and Boost.MPL. 
> 
> IMHO the introduction of another set of placeholders is more confusing.
> If we are to discriminate here, we can do it via namespaces - and of course 
> one day it is std::_1 for all of us. 
> 
> Just because your library is the first to use _a, _b, _c

It isn't.  Boost.Phoenix uses _a, _b, etc for local
variables.

> what does that mean 
> for future (boost) libraries that use some kind of placeholders?
> Do they have to use _aa, _bb, etc.? 
> To me placeholders are such a natural concept I do not care about having 
> some kind of "deja vu" here. To the contrary: The meaning (placeholder) is 
> identical so we should use identical names.
> 

It isn't exactly identical.  The names _1, _2
carry extra meaning about how they are substituted
which doesn't make sense for my library.

>> I eventually decided that since the placeholders represented named
>> parameters instead of positional parameters, letters were more 
>> appropriate than numbers. 
> 
> Indeed the naming is arbitrary. Starting from the same observation (_1 is 
> already available in boost::*) I draw the opposite conclusion:
> Use these names for the sake of symmetry and hope for convergence of 
> concepts over the years.
> 
> @Review Master: Should I miss the end date for reviews, take this as my mini 
> subset of a review: I'd prefer _1, _2 instead of _a, _b.
> 

You are of course free to disagree with
my decision, but I'm not going to change it.

In Christ,
Steven Watanabe