Question

I have following code to merge two std::maps.

template <typename key, typename value>
  void merge_maps(std::map<key, value>& one, const std::map<key, value>& another,
    boost::function2<value, value, value> aggregate)
  {
    // MERGING. aggregate is called if key exists in both maps
  }

I have some struct like this.

  struct foo {
    int bar;
    foo operator+(const foo& other) const;
  };

I tries to merge two std::map<std::wstring, foo> one, another using foo::operator+ which I passed using boost::lambda, but get compilation error.

  merge_maps(one, another, _1+_2); // MSCV9.0 cannot deduce template argument for lambda there

Help me please. What I’m doing wrong?

Answer 1

Solved. It was needed to specify lambda return type. MSVC instantiates template without any troubles.

merge_maps(one, another, ret<foo>(_1+_2));