Re: hasMember
On Dec 9, 7:01 am, Paavo Helde <myfirstn...@osa.pri.ee> wrote:
Andrea Crotti <andrea.crott...@gmail.com> wrote innews:m11v5rrcno.fsf@ip1-201.halifax.rwth-aachen.de:
Jeff Flinn <TriumphSprint2...@hotmail.com> writes:
To avoid the memory allocation and ownership issues use
boost::optional.
#include <boost/optional.hpp>
typedef boost::optional<int> optional_int;
optional_int Cont::getValue(int idx) const
{
std::map<int, int>::const_iterator itr = content.find(idx);
return (itr != cont.end())? itr->second : optional_int();
}
and:
if(optional_int i = obj.getValue(idx)) // safe bool idiom
{
int x = *i + 123; // deref for value
}
Using exceptions in this case could be good?
Seems out of place for the use you've described, given what little
info you've provided.
Interesting the optional_int, but I can't use boost...
I'm sure boost::optional is quite easy (and instructive) to implement by
yourself.
Except that he really needs optional<int&>. Which in turn means
partial specialization for reference types, and the partial
specialization would be nothing more than a wrapper around
a pointer. There's really no point in not using a pointer to
begin with.
[...]
Have you considered the simple way of having another output parameter in
addition to the return value?
bool Cont::getValue(int idx, int& value_out) const
{
std::map<int, int>::const_iterator itr = content.find(idx);
if (itr != content.end()) {
value_out = itr->second;
return true;
} else {
return false;
}
}
// ...
int x;
if (obj.getValue(idx, x)) {
// x found and valid, do something with x
}
This has the drawback that the lexical scope of x is too broad, but if
this is a very low-level class used only by a couple of slightly higher-
level classes this might be OK.
If his functions are reasonably small, the increased lexical
scope is not a problem. Defining an uninitialized int is more
bothersome.
But what's wrong with the pointer solution? That's what I'd
like to know. It's certainly the most idiomatic solution for
this problem.
--
James Kanze