Re: [boost] Checking for return types (result_of) - redux..

Subject: Re: [boost] Checking for return types (result_of) - redux..
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-08-21 11:04:39

Edward Grace wrote:
> On 21 Aug 2009, at 15:29, Steven Watanabe wrote:
>
> It seems quite unedifying having to make sure the user adds some,
> apparently arbitrary, magic typedef to their functors in order to
> make sure it works.
>
> My original motivation was to form a helpful compile time assert for
> the user, which I thought would be good practise. It appears all this
> does is to shift a conceptually straightforward problem (make sure
> your functor/function returns something) to an even more obscure one
> "ordinary functions are fine but make sure you define a return_type
> typedef in your functions oh.. and make sure the return type of the
> operator()() is the same as that... " Then I have to add a way of
> sanely catching if they have not done this - I doubt I can...  Crazy!

Why not define your code to take a boost::function<double(/* whatever goes here */)>?

Is the argument list variable?  If so, aren't you already aware of that variance to use in the function type argument for boost::function?

If that doesn't work, you'll need all of the crazy stuff that template argument packs will solve conveniently to accept N arguments:

   template <class R>
   R
   foo(boost::function<R()>);

   template <class R, class Arg1>
   R
   foo(boost::function<R(Arg1)>);

   template <class R, class Arg1, class Arg2>
   R
   foo(boost::function<R(Arg1, Arg2)>);

etc.

HTH,

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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