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Momchil Velikov
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 Posted: Sun Sep 21, 2003 10:12 am Post subject: Cannot invoke a templated ctor |
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The following program produces error at the definition of ``b''. However it
compiles fine the second (supposedly equivalent) form of the templated
constructor. Why the two alternatives aren't equivalent ?
template<class Obj>
struct ptr_to_member
{
typedef void (Obj::* type) ();
};
struct A
{
A (void (*fn) ())
{
}
#if 1
template<class Obj>
A (typename ptr_to_member <Obj>::type fn)
{
}
#else
template<class Obj>
A (void (Obj::* fn) ())
{
}
#endif
};
void foo ()
{
}
struct bar
{
void baz ()
{
}
};
A a (foo);
A b (&bar::baz);
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Graeme Prentice
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| Posted: Wed Sep 24, 2003 10:27 pm Post subject: Re: Cannot invoke a templated ctor |
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On 21 Sep 2003 06:12:58 -0400, [email]velco (AT) fadata (DOT) bg[/email] (Momchil Velikov) wrote:
| Quote: | The following program produces error at the definition of ``b''. However it
compiles fine the second (supposedly equivalent) form of the templated
constructor. Why the two alternatives aren't equivalent ?
|
Because ptr_to_member <Obj> is a non-deduced context - a nested name
specifier is a non deduced context - 14.8.2.4 para 4. The compiler
won't deduce Obj to be bar because the standard doesn't allow it to.
It was discussed here recently
http://makeashorterlink.com/?I2B622EF5
Graeme
| Quote: |
template<class Obj
struct ptr_to_member
{
typedef void (Obj::* type) ();
};
struct A
{
A (void (*fn) ())
{
}
#if 1
template
A (typename ptr_to_member
{
}
#else
template
A (void (Obj::* fn) ())
{
}
#endif
};
void foo ()
{
}
struct bar
{
void baz ()
{
}
};
A a (foo);
A b (&bar::baz);
|
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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