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Maitre Bart
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 Posted: Wed Nov 15, 2006 6:35 am Post subject: template no-match |
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I made a functor that outputs a custom-formatted string given a pair as
input:
class pair2string
{
public:
pair2string() : _sep(" => ") {}
pair2string(const string& sep_) : _sep(sep_) {}
template <typename F, typename S>
string operator()(pair<F,S>& p_) const
{
ostringstream oss;
oss << p_.first << _sep << p_.second;
return oss.str();
}
private:
const string _sep;
};
It works fine for:
cout << pair2string()(*m.begin()) << "\n";
where m is a map<string,int> .
But if one of the pair arguments is a pair, there is a no-match, as
for:
cout << pair2string()(make_pair("test",*m.begin())) << "\n";
So, I tried to add this overload in my class to solve the no-match:
template <typename F, typename SF, typename SS>
string operator()(pair<F,pair<SF,SS> >& p_) const
{
ostringstream oss;
oss << p_.first << _sep << pair2string(_sep)(p_.second);
return oss.str();
}
But I still get a no-match from the compiler. Anyone has any idea why
and have a solution to the no-match?
In the end, I'd like to overload the 2 other possibilities:
template <typename FF, typename FS>
string operator()(pair<pair<FF,FS>,S>& p_) const
{
ostringstream oss;
oss << pair2string(_sep)(p_.first) << _sep << p_.second;
return oss.str();
}
template <typename FF, typename FS, typename SF, typename SS>
string operator()(pair<pair<FF,FS>,pair<SF,SS> >& p_) const
{
ostringstream oss;
oss << pair2string(_sep)(p_.first) << _sep <<
pair2string(_sep)(p_.second);
return oss.str();
}
Thank you for helping me.
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dasjotre
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| Posted: Thu Nov 16, 2006 3:55 am Post subject: Re: template no-match |
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Maitre Bart wrote:
| Quote: | I made a functor that outputs a custom-formatted string given a pair as
input:
class pair2string
{
public:
pair2string() : _sep(" => ") {}
pair2string(const string& sep_) : _sep(sep_) {}
template <typename F, typename S
string operator()(pair<F,S>& p_) const
{
ostringstream oss;
oss << p_.first << _sep << p_.second;
return oss.str();
}
private:
const string _sep;
};
It works fine for:
cout << pair2string()(*m.begin()) << "\n";
where m is a map<string,int> .
But if one of the pair arguments is a pair, there is a no-match, as
for:
cout << pair2string()(make_pair("test",*m.begin())) << "\n";
|
first problem is that your pair2string::operator() takes a
non const and make_pair returns temporary which can only be
bound to a const reference
second problem is that you don't have an operator where
F or S can be pairs and there is no ostream << specialization
for pairs
| Quote: |
So, I tried to add this overload in my class to solve the no-match:
template <typename F, typename SF, typename SS
string operator()(pair<F,pair<SF,SS> >& p_) const
{
ostringstream oss;
oss << p_.first << _sep << pair2string(_sep)(p_.second);
return oss.str();
}
But I still get a no-match from the compiler. Anyone has any idea why
and have a solution to the no-match?
In the end, I'd like to overload the 2 other possibilities:
template <typename FF, typename FS
string operator()(pair<pair<FF,FS>,S>& p_) const
{
ostringstream oss;
oss << pair2string(_sep)(p_.first) << _sep << p_.second;
return oss.str();
}
template <typename FF, typename FS, typename SF, typename SS
string operator()(pair<pair<FF,FS>,pair<SF,SS> >& p_) const
{
ostringstream oss;
oss << pair2string(_sep)(p_.first) << _sep
pair2string(_sep)(p_.second);
return oss.str();
}
|
the short version:
(if you have a ostream<< defined for ::std::string)
class pair2string
{
public:
pair2string() : _sep(" => ") {}
pair2string(const ::std::string & sep_) : _sep(sep_) {}
template <typename T>
::std::string operator()(T const & p_) const
{
::std::ostringstream oss;
oss << p_;
return oss.str();
}
template <typename F, typename S>
::std::string operator()(::std::pair<F,S> const & p_) const
{
::std::ostringstream oss;
pair2string p2s(_sep);
oss << p2s(p_.first) << _sep << p2s(p_.second);
return oss.str();
}
private:
const ::std::string _sep;
};
--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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