Re: [boost] [TypeErasure]

Subject: Re: [boost] [TypeErasure]
From: Markus Werle (numerical.simulation_at_[hidden])
Date: 2012-07-23 14:17:43

Steven Watanabe wrote:

> AMDG

[*slightly* off-topic: Does that mean Ad maiorem Dei gloriam?]

> 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 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.

> 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.

Markus