Re: CMap and struct
"Vahid" wrote:
Thanks a lot guys for your suggestions. Since I'm not used to standard
library (compared to MFC), I picked CMap right away. And before
reading your messages, I had come up with the following which compiled
ok:
struct SDataType {
unsigned long nNamespace;
unsigned long nDataType;
SDataType& operator=(SDataType s2) { nNamespace = s2.nNamespace;
nDataType = s2.nDataType; return *this; }
bool operator==(SDataType s2) const { return ((nNamespace ==
s2.nNamespace) && (nDataType == s2.nDataType)); }
};
template<> AFX_INLINE UINT AFXAPI HashKey(SDataType& key)
{
return HashKey((DWORD_PTR) key.nNamespace) + HashKey ((DWORD_PTR)
key.nDataType);
}
Arman, how do you compare this with your suggestion. As you see, I do
not use reference parameters here.
Thanks again,
Vahid.
Vahid,
It's ok to have no const references in this specific case because the fields
of the struct are not so large; my point is they are primitive types and
copying will not be inefficient.
One point about assignment operator. Here you'd rather either to have const
refeneces or to have no assignment operator at all [as noticed David]. The
problem [well not so strictly] is that in the assignment operator you are
invoking the copy-ctor when passing arguments [rhs values] to the operator.
Here will take place a bitwise-copy (shallow copy) of arguments [and then you
copy them again [though member-wise (deep) copy] inside the operator. So the
logic and purpose are harmed. No technical issue.
HashKey issue.
Yes you can do that; it's ok to overload the default behaviour of the MFC
HashKey global function. Another way to go, shown im my first reply, is to
overload the DWORD operator for the struct. Though your way is more specific.
So keep it.
--
======
Arman
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