Re: [boost] Boost.Algorithm design question

Subject: Re: [boost] Boost.Algorithm design question
From: Peter Dimov (pdimov_at_[hidden])
Date: 2011-11-02 06:25:23

Andrew Sutton wrote:
> >> But I'm not requiring both sides to be the same -- only related.
> >
> > I'm not sure how you're doing that. I thought that this was about using 
> > the
> > EqualityComparable standard requirement, which does require the two 
> > sides of
> > == to be of the same type, and == to be an equivalence relation.
>
> The standard does not say that about EqualityComparable. 17.6.3.1
> [utility.arg.requirements] only says that a == b is convertible to
> bool and is an equivalence relation.

17.6.3.1? It's in 20.1.1 [lib.equalitycomparable] in C++03 and in 20.2.1 
[utility.arg.requirements] in N3225. In C++03, the preceding text states:

In Table 28, T is a type to be supplied by a C + + program instantiating a 
template, a, b and c are values of type T.

In N3225, the text states that

In these tables, T is an object or reference type to be supplied by a C++ 
program instantiating a template; a, b, and c are values of type (possibly 
const) T; s and t are modifiable lvalues of type T; u denotes an identifier; 
rv is an rvalue of type T; and v is an lvalue of type (possibly const) T or 
an rvalue of type const T.

It makes sense, too; the table describes what it means for T to be 
EqualityComparable. What would be EqualityComparable if a, b and c were 
arbitrary?