[Boost-users] Passing lambda placeholders to functions

Subject: [Boost-users] Passing lambda placeholders to functions
From: Zachary Turner (divisortheory_at_[hidden])
Date: 2009-06-22 19:10:11

It seems very simple, but it's not compiling.

int translate(const std::string& str)
{
   return 0;
}

//all required using declarations are present but omitted for brevity
//
options_description options;
variables_map values;
int i;

options.add_options()
   ("test", value<std::string>()->notifier(var(i) = translate(_1)));

I get the following error:

'translate': cannot convert parameter 1 from
'boost::lambda::placeholder1_type' to 'std::string'.  No user defined
conversion operator available that can perform this conversion, or the
operator cannot be called.

Is this type of usage unsupported for some reason?  If I change the
variable declaration and the add_options() call to the following it
works fine:

std::string s

options.add_options()
   ("test", value<std::string>()->notifier(var(s) = _1));