🚀 go-pugleaf

vandevod@cs.rpi.edu (David Vandevoorde) writes:

>>>>>> "FH" == Fergus Henderson <fjh@munta.cs.mu.OZ.AU> writes:
>[...]
>FH> template <class T, class S> T cast_d(S &s) 	
>	{ return dynamic_cast<T>s; }
>FH> template <class T, class S> T cast_d(const S &s) 
>	{ return dynamic_cast<T>s; }
>FH> template <class T, class S> T cast_d(volatile S &s)
>FH>	{ return dynamic_cast<T>s; }
>FH> template <class T, class S> T cast_d(const volatile S &s)
>FH> 	{ return dynamic_cast<T>s; }
>
>Isn't the last one sufficient?

No, because 5.2.6[expr.cast.dynamic]/1 states that "dynamic_cast shall
not cast away constness".  If you only defined the last one, then code
such as

	class Foo : public Bar { /* ... */ };
	void f(Bar& x) {
		cast_d<Foo&>(x);
	}

would be ill-formed, because it would instantiate

	cast_d<Foo&, Bar> Foo& cast_d(const volatile Bar &s)
	{ return dynaic_cast<Foo&>(s); }

and this dynamic_cast would be casting away constness.

Incidentally, 5.2.6 would seem to imply that dynamic_cast *is* allowed
to cast away volatileness, but I think that is a mistake in the current
draft.

>(and aren't parentheses required in `dynamic_cast<T>(s)'?).

Yes, they are -- thanks for correcting that error.

--
Fergus Henderson             	WWW: http://www.cs.mu.oz.au/~fjh
fjh@cs.mu.oz.au              	PGP: finger fjh@128.250.37.3
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