Minor bug gets bigger? (was Re: Potential minor bu revealed?)

[Phil Edwards]

On Tue, May 07, 2002 at 03:26:38PM -0400, Stephen M. Webb wrote:
> stephen_[176]>  g++ -o br br.cc
> br.cc: In function `int main(int, char**)':
> br.cc:9: conversion from `int' to non-scalar type `std::_Bit_reference' 
>     requested
> 
> This message is a little confusing to say the least.  I get a more 
> relevant message if I remove the <iostream> inclusion.

What version are you using?  The _Bit_reference class is in stl_bvector.h,
which doesn't get included with only <algorithm> and <iostream>.  Using the
current 3.1 prerelease, I get this error instead:

> stephen_[177]> g++ -o br1 br1.cc
> br1.cc: In function `int main(int, char**)':
> br1.cc:8: no matching function for call to `swap(int&, const int&)'

Now, if I also include <vector>, then the weird error appears.  This makes
sense to me and my limited understanding of template function overloading:
the compiler never instantiates the template form of std::swap, since it
already sees a non-template function.  Which unfortunately happens to be
for a class which nobody would ever use.

Changing your test case to specifically use the template version gives
various const-related errors, as desired.


> Other than the confusing error message, would this indicate a potential 
> problem in vector<bool>?

Well, it wouldn't be the first problem with vector<bool>...  anyhow,
I note that the standard doesn't specify a non-template std::swap() for
vector's "bit reference" class.  But we have one.  The standard /does/
specify a static non-template member function, std::vector::swap, for the
bit reference class, but we /don't/ have one.

Moving the _Bit_reference's swap down inside the vector<bool> specialization,
like the standard says, makes this problem go away.  I'll post a patch
after 3.1 is out.


Phil

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