Getting the return type of a function call without actually running it

[Qiyamah]

Hi fellows,

I am working on a way to dispatch according to the return type of a function call.

I asked a similar question here:

How to calculate the typeof an expression without actually running it?

Hi, I would like to calculate the typeof an expression without running it. For example: function f(x::Int) y = x+3 if x > 0 y+=1 else y-=3 end x+y end for example in a macro i am working with the expressions of this function and is there a way to calculate y+=1 to be type of Int? Thanks

I am asking it again in case something in julia may have changed.

[rdeits]

Nothing fundamental, no. It’s still impossible to do in general. Can you explain more about what you’re actually trying to accomplish? Perhaps then we can be more helpful.

[mauro3]

@Qiyamah

I am working on a way to dispatch according to the return type of a function call.

Maybe of historical interest: GitHub - mauro3/Traits.jl: Exploration of traits in Julia. This package was able to do this, but does not work anymore due to more stringent restrictions on generated functions.

[traktofon]

As others have said, it’s impossible to do in general, but faced with a similar problem in my (unregistered) package ComputedArrays.jl I am using the following (in julia v0.7):

T = Union{Base.return_types(fn, argtypes)...}

where argtypes is a tuple with the types of the arguments to the function fn. See ComputedArrays.jl/ComputedArrays.jl at for07 · traktofon/ComputedArrays.jl · GitHub.

[gdkrmr]

What about

f(x) = x
Base.return_types(f, (Int64,))