Re: [boost] Geometry/Vector Lib

----Original Message----
From: boost-bounces@lists.boost.org
[mailto:boost-bounces@lists.boost.org] On Behalf Of Frank Birbacher
Sent: 05 October 2006 10:00 To: boost@lists.boost.org
Subject: Re: [boost] Geometry/Vector Lib

> Hi!
> 
> Jason Hise schrieb:
>> vec[0] = 42;
>> vec[_x] = 42; // does the same thing
> 
> "_x" is not allowed as a variable name. 
Yes it is.  17.4.3.1.2 [lib.global.names] in the standard says:
- Each name that contains a double underscore (_ _) or begins with an
underscore followed by an uppercase letter (2.11) is reserved to the
implementation for any use.
- Each name that begins with an underscore is reserved to the
implementation for use as a name in the global namespace.

_x is legal if it is defined in (eg) boost::geometry and brought in via
a using statement.
The real problem is that leading _ is a fairly common convention for
"member variable", and as you mention below, a member named 'x' in a
mathematical context is not inconceivable!



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Martin Bonner
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