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I want to have a std::unordered_map<std::string,MyClass*()> variable. But - when I try instantiating that, I get an error message, deep inside, which is essentially:

/usr/include/c++/4.9/bits/stl_pair.h(102): error: a function type is not allowed here
          detected during:
            instantiation of class "std::pair<_T1, _T2> [with _T1=const std::string, _T2=MyClass *()]"

I'm pretty sure this isn't due to a bug of mine. I've browsed around the site and noticed a link to LWG issue 2051 making std::pair too restrictive. Is that really what I'm seeing? If so, what should I do to work around it? Use a wrapper class no data and operator() maybe? std::function?

T.C.
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einpoklum
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    To be clear, you want to map from string to pointer-to-function-taking-no-arguments-and-returning-pointer-to-MyClass ? If so, then change the second argument to `MyClass *(*)()` – M.M Dec 21 '15 at 23:45
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    I don't see how issue 2051 is related – M.M Dec 21 '15 at 23:46
  • I don't think a container of functions is legal - [container.requirements.general] says that contains store *objects*. So to implement a container of functions you actually have to have a container of function pointers (or a class that wraps a function pointer, like `std::function`, or functor objects). – M.M Dec 21 '15 at 23:52
  • @M.M: FIxed that. Now I'll go look if that problem isn't actually in my code somewhere. – einpoklum Dec 21 '15 at 23:53
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    your error message doesn't correspond to your code... `_T2` would not be `MyClass *()` in the updated code. If you still have trouble then post a MCVE. [Working example](http://goo.gl/EoiHqS) – M.M Dec 21 '15 at 23:53

1 Answers1

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If you want to have a map from a string to a MyClass pointer, you have to declare: 

 std::unordered_map<std::string,MyClass*> x;

But if you want to have a map to a function pointer to a function returning a pointer to MyClass you could consider: 

std::unordered_map<std::string,MyClass*(*)()> x;
Christophe
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  • WIll check to see if that was the issue or if I just misquoted the definition (there's some `using = ` involved which I've removed). – einpoklum Dec 21 '15 at 23:54