If I have a function with optional arguments like
add(a=2;b=3)=a+b
is it possible to find out what the defaults are?
I don’t think so. Default arguments just result in Julia creating extra methods for your function. For example:
julia> f(x=5) = x + 1
f (generic function with 2 methods)
julia> methods(f)
# 2 methods for generic function "f":
f() in Main at REPL[1]:1
f(x) in Main at REPL[1]:1
Defining f(x=5) = ... actually defined two methods:
f(x) = ...
f() = f(5)
so inside the inner method (f(x)), there’s no indication whether the x it received was a default argument or not. Keyword arguments do something similar by creating an inner function without keyword arguments.
What are you actually trying to do? Perhaps there’s another way.
I have a simulation with certain default parameters. Then I want to double and halve these parameters and record the results. I can do this simply by putting all the parameters in a list but I wondered if I can also do it via writing something like
add(a=defaults(add).a*2)
or something.
Ah, no, that’s not possible. After all, you could have arbitrarily many methods named add, so what would defaults(add) possibly return?
Instead, if you put your parameters in a struct and pass that struct to your function, manipulating the parameters as a group becomes much easier. Check out https://github.com/mauro3/Parameters.jl for some macros to make constructing parameter structs easier.
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