Getfield from package / module

General Usage
1

In a package I created, I am trying to call a function with a string, and using getfield, return a function from another package. The other package has been properly added to my package, and I could use the functions if called like a = Poisson(5)

The code below works, if I bring in the entire package with using. If I uncomment out the part of the using so only Poisson, Gamma, and Normal are allowed, then calling MYcompare.foo("Poisson") returns an error that Distributions is not defined.

I am trying to understand while restricting to those distributions won’t work but bringing in everything does.

module MYcompare
    using Distributions #: Poisson, Gamma, Normal
    export foo

    function foo(str)
        s = Symbol(str)
        f = getfield(Distributions,s)
        return f(5)
    end

end
2

Here is what I think is the reason that Distributions is not defined:

I re-read the manual on the using statement. Specifying which names to be brought in doesn’t bring in the name of the module. Changing the code above to:

using Distributions: Distributions, Poisson, Gamma, Normal

works!

3

Yes, that’s the reason.

That said, note that this usage is not idiomatic and will generate suboptimal code.

4

Why is it suboptimal? It looks legit.

5

Types won’t be inferred.

2 Likes
6

Thank you for the responses. I am using this to create a way to work with a large number of tests to compare the results between the Julia code and our in house c# so performance is not crucial. The Julia code that is eventually called follows idiomatic Julia and I think is type stable.

I’ve been using matlab for 20 years and then forced to use R for the last 5. I am in complete awe that I was able as a new user with Julia:

  • Take a TOML file generated from another system with inputs and outputs
  • Convert the TOML to a dictionary.
  • Map some of those inputs to Julia Functions (the above code)
  • Then convert the dictionary to a named tuple
  • which is then splatted as the optional arguments to a struct constructor
  • run the models/simulations with this composite type
  • compare the results of the Julia simulations to those in the TOML file

All done in a ridiculously clear and small amount of code.

3 Likes