Hi,
If I have a vector of strings
vector<string> v;
v.push_back("One");
v.push_back("Two");
v.push_back("Three");
v.push_back("Four");
v.push_back("Five");
and define arithmetic action plus like this:
namespace boost {
namespace lambda {
struct plain_return_type_2<arithmetic_action<plus_action>,
std::string, std::string> {
typedef std::string type;
};
}
}
then the following code works just fine:
cout << accumulate(v.begin()+1, v.end(), v.front(), _1 + string(", ") +
_2) << endl;
and the following also works wonderfully:
int i = 1;
cout << accumulate(v.begin()+1, v.end(), v.front(), _1 +
bind(constructor<string>(), var(i)++, ' ') + _2) << endl;
Now, if I want to use if_then_else_return as shown below, it fails
miserably, producing a huge error message:
cout << accumulate(v.begin(), v.end(), string(), if_then_else_return(_1
== string(),
_1,
_1 + bind(constructor<string>(), var(i)++, ' ') + _2)) << endl;
Now for the questions:
What is the proper way to use if_then_else_return? Why do I need to
define a separate arithmetic action for strings, even though they are a
common library type? Is there a way to say the most intuitive:
cout << accumulate(v.begin()+1, v.end(), v.front(), _1 + ", " + _2) <<
endl;
Is there way to do more intuitive:
cout << accumulate(v.begin()+1, v.end(), v.front(), _1 + string(i++, '
') + _2) << endl;
Thank you for your help.
Robert Ioffe
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