[julia-users] Runtime inference of a function's return type

[Fábio Cardeal]

Is there a good way to find a function's return type with only the types of 
its arguments?
I mean, I can do something like:


 codetyp(code) = code.args[3].typ

 function returntype(f::Function, types::Tuple)
     if isgeneric(f) 
         mapreduce(codetyp, Union, code_typed(f, types))::Type
     else
         Any
     end
 end

 function returntype(f, types::Tuple)
     returntype(call, (typeof(f), types...))
 end



 julia> returntype(identity, (Int,))
 Int64

 julia> returntype(returntype, (Function, Tuple))
 Type{T} 


But is this really reliable? Is there a way to do this other than directly 
accessing the function's internals?