Re: Typedef allows redefinition of names?

From:
Joe Greer <jgreer@doubletake.com>
Newsgroups:
comp.lang.c++
Date:
Mon, 5 Nov 2007 21:54:47 +0100 (CET)
Message-ID:
<Xns99DFA1E0BE974jgreerdoubletakecom@194.177.96.78>
Ken Camann <kjcamann@gmail.com> wrote in news:1194293869.860459.137680@
57g2000hsv.googlegroups.com:

I was a bit surprised to find that my compiler (MSVC++) actually
accepts the following as legal. It cleans up the code very nicely,
but I am sort of confused about some of the finer points of how the
naming and template systems interact in a compiler. Does the
following always work?

In Vector3.h, I have this class

namespace Geometry {

termplate<typename NumericType>
class Vector3
{
...
};

}

In another file, Triangle.h, I have

#include <Vector3.h>

namespace Geometry {

template<typename NumericType>
class Triangle
{
public:
     typedef Vector3<NumericType> Vector3;

    //Then I go on to use Vector3 instead of Vector3<NumericType>
};

}

Like I said, I was pretty surprised it let me take the "root" part of
the template name Vector3<NumericType> and redefine it as a specific
type, namely the specific type that inherits the template type from
the class that it belongs to. Needless to say, if I type in
Vector3<NumericType> after the typedef this produces an error, since
the symbol Vector3 = Vector3<NumericType> already.


Interesting...

I suspect that it is because there is no Vector3 defined at that scope
(within the class). So, what you have defined is Geometry::Triangle
<NumericType>::Vector3 and that doesn't conflict with Geometry::Vector3
<>.

joe

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