🚀 go-pugleaf

sdm@cs.brown.edu (Scott Meyers) writes:
|In article <1992Oct31.213412.356@frumious.uucp> uunet.ca!frumious!pat writes:
|| In my understanding, one of the principles of C++ is that any construct
|| which has the potential to violate the type system is illegal unless
|| an explicit cast is used.  So the explicit cast should be required in
|| the call to f() - not because the compiler knows there is a problem,
|| just because it _doesn't_ know there _isn't_.  This is exactly why
|| you need an explicit cast to convert a pointer to base class to
|| pointer to derived class, but not to cast from derived to base.
|
|However, you don't need an explicit cast to go from a T* to a void*.

Converting a T* to a void*, by itself, doesn't violate the type system,
because a void* can point to anything.

It's the conversion from a void* to a T* that might violate the type
system, because the void* might not point to a T.  Hence the explicit
cast is required for this conversion.


|Hence, given that this is legal,
|
|    T *p;
|    void *q = p;
|
|is there a good reason why this isn't?
|
|    void f(T*);
|    void (*pf)(void*) = f;

Because it involves an implicit conversion of void* to T*
(_not_ T* to void*).

-- 
Patrick Smith
uunet.ca!frumious!pat
pat%frumious.uucp@uunet.ca