Wondering about this… template argument deduction succeeds for the explicitly-typed variable, fails in the auto case. (Also, it succeeds either way for an equivalently-typed unary operator template).<\/p>\n
\r\ntemplate \r\nstruct Foo\r\n{\r\n T m_t;\r\n};\r\n\r\ntemplate \r\nFoo operator\/=(Foo foo, function(T)> fn)\r\n{\r\n return fn(foo.m_t);\r\n}\r\n\r\nvoid mystery()\r\n{\r\n auto foo = Foo{1};\r\n\r\n \/\/ this works...\r\n function(int)> f1 = [] (int i) { return Foo{i}; };\r\n auto bar1 = foo \/= f1;\r\n\r\n \/\/ this doesn't\r\n auto f2 = [] (int i) { return Foo{i}; };\r\n auto bar2 = foo \/= f2;\r\n\r\n \/\/ clang++ 3.3-16ubuntu1 says:\r\n \/\/ file:line:col: error: no viable overloaded '\/='\r\n \/\/ auto bar2 = foo \/= f2;\r\n \/\/ ~~~ ^ ~~\r\n \r\n \/\/ file:line:col: note: candidate template ignored: could not match\r\n \/\/ 'function (type-parameter-0-0)>' against\r\n \/\/ ''\r\n \/\/ Foo operator\/=(Foo foo, std::function(T)> fn)\r\n \/\/ ^\r\n}\r\n<\/pre>\n