Re: [boost] [proto][design] why unary_expr, binary_expr; but no nullary_expr?

Subject: Re: [boost] [proto][design] why unary_expr, binary_expr; but no nullary_expr?
From: Eric Niebler (eric_at_[hidden])
Date: 2008-12-14 02:58:12

Eric Niebler wrote:
> Larry Evans wrote:
>> Although there's unary_expr<Tag,*>, binary_expr<tag,*,*>
>> in traits.hpp there's no nullary_expr<Tag>.  I realize
>> this would be a replacement to the current terminal template
>> but with a user specified tag.  After all,
>> if a user specified tag for n-ary (where n>0) expressions
>> *is* desirable, why is a user specified tag for 0-ary
>> expressions *not* desirable?  
> <snip>
> 
> Mostly because I couldn't think of a use case at the time. There's 
> nothing in Proto's design that would prohibit a 0-ary expression from 
> having a tag type other than tag::terminal, but I bet there are some 
> places in the code that make that assumption. They would all need to be 
> hunted down and fixed. Probably not too hard. 

This is now implemented on trunk.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com