Use of `Ref` in broadcasting user-defined functions

New to Julia
1

Hello,

I would like to apply a function that I’ve created to an array/range. Let me use a simplified version of my code to illustrate my question. It starts defining a structure for parameters, something like:

using Parameters

@with_kw struct myParams
   α::Float64 = 0.5
   β::Float64 = 0.5
end

p = myParams()

Then I create a function, like:

function myf(x::Float64, p::myParams)::Float64
    @unpack α, β = p

    return β*x^α
end

Now I want to apply this function, with a particular instance of myParams, to a range or array. I could do it using a for loop, but that seems not very julian. Using broadcasting, I thought of writing this:

@time myf.(range(0.0, stop = 100.0), p)

It gives an error:

MethodError: no method matching length(::myParams)
Closest candidates are:
  length(!Matched::DataStructures.IntSet) at /home/arnau/.julia/packages/DataStructures/ixwFs/src/int_set.jl:191
  length(!Matched::DataStructures.DiBitVector) at /home/arnau/.julia/packages/DataStructures/ixwFs/src/dibit_vector.jl:40
  length(!Matched::ExponentialBackOff) at error.jl:259
  ...
_similar_for(::UnitRange{Int64}, ::Type{Any}, ::myParams, ::Base.HasLength) at array.jl:597
_collect(::UnitRange{Int64}, ::myParams, ::Base.HasEltype, ::Base.HasLength) at array.jl:630
collect(::myParams) at array.jl:624
broadcastable(::myParams) at broadcast.jl:682
broadcasted(::Function, ::StepRangeLen{Float64,Base.TwicePrecision{Float64},Base.TwicePrecision{Float64}}, ::myParams) at broadcast.jl:1261
top-level scope at timing.jl:174 [inlined]
top-level scope at Tests.jl:0

I’ve tried this, and it works:

@time myf.(range(0.0, stop = 100.0), Ref(p))

However, after reading the documentation for Ref, I’m not sure I’m doing the right thing here. Any help?

Thank you.

2

You are using Ref in broadcasting correctly. Ref inhibits broadcasting from iterating over the fields of p.

3

If you want your type to always act as a scalar, you can tell the broadcasting machinery to do that:

Broadcast.broadcastable(mp::MyParams) = Ref(mp)

Then myf.(range, p) should work.

BTW, it’s a strong convention in Julia to make type names UpperCamelCase. So for clarity, you should probably call your type MyParams instead of myParams.

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