Member function template using boost::function

Question

The following TestClass works:

#include <iostream> #include <boost/function.hpp> #include <boost/bind.hpp> void ext_fun(const float f, int i) { std::cout << f << '\t' << i << std::endl; } template <typename T> class TestClass { public: boost::function <void (const T)> test_fun; }; int main() { TestClass<float> tt; tt.test_fun = std::bind(ext_fun, std::placeholders::_1, 10); tt.test_fun(2.1); return(0); }

However, I would prefer to define test_fun as a member function template, i.e., something like

class TestClass { public: template <typename T> boost::function <void (const T)> test_fun; };

But if I do it, I get this compiler error: "error: data member ‘test_fun’ cannot be a member template"

Is it possible to define a member function template using a boost::function? If yes, how?

Thank you

--Matteo

Sorry, that doesn't make sense - that's not what "function template" means. You're asking the equivalent of "can I turn struct Foo { int a; }; into struct Foo { template <typename T> T a; };", which you cannot. — Kerrek SB
– Kerrek SB, Commented Jan 11, 2014 at 6:22
@Kerrek SB I was referring to something like the very first example here, or the question here, but using the boost::function — Matteo M.
– Matteo M., Commented Jan 11, 2014 at 7:34

sh03 · Accepted Answer · 2014-01-11 07:53:22Z

1

Is it possible to define a member function template using a boost::function? If yes, how?

I think you have a little bit of confusion going on here. A function template is, first of all, a function. Your test_fun is not a function, it's a member object of the class TestClass. Member objects can't be templatized in C++.

answered Jan 11, 2014 at 7:53

sh03

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2 Comments

Matteo M. Over a year ago

Ok, so the point is: class methods can be templatized (like here), but if I use boost::function I do not actually have a method but a member object instead. So it cannot be templatized. Is this correct?

sh03 Over a year ago

@MatteoM., the "class method" terminology doesn't exists in C++: you should get used to "member function" instead. But yeah, the concept is correct. A boost::function is a class type, which leads the declaration boost::function <void (const T)> test_fun; to be an object, which cannot be templatized.

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