Re: [boost] [Variant] Documentation Questions/Notes

Subject: Re: [boost] [Variant] Documentation Questions/Notes
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-11-02 11:48:16

on Fri Nov 02 2012, Brian Simpson <wheber-AT-hotmail.com> wrote:

> Dave Abrahams <dave <at> boostpro.com> writes:
>
>> 
>>  <snip>
>> 
>> - Do the semantics for are_strict_equals at
>>   http://www.boost.org/doc/libs/1_51_0/doc/html/variant/tutorial.html
>>   differ from those of the built-in equality operator?
>> 
>
> The built-in equality operator compares two instances of identically-typed
> variant.  As a binary visitor, however, are_strict_equals can compare
> non-identically-typed variants.

Interesting.  hard to think of that as "strict," though.

> boost::variant<int, std::string> v1("hello");
> boost::variant<int, std::string> v2("g'bye");
> boost::variant<double, std::string> v3("hello");
> assert(!(v1 == v2));
> assert(v1 == v3);//compile error
> assert(boost::apply_visitor(are_strict_equals(), v1, v3));
>
> Interestingly, it looks as if variant goes the extra mile to "prevent comparison
> with foreign types" (that's a comment from variant.hpp).  I wonder why.

Yeah.  FWIW, while I do appreciate the answers, my *main* intention in
posting these comments was to get the maintainer to fix the
documentation.  Hint, hint :-)

-- 
Dave Abrahams
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