Metaprogamming

General Usage
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1

Hi there,

I am writing a module with dozens of MyType like structure (as below), that all belong to an Abstract super type. I would like to be able to write a meta constructor (roughly sketched below). Is it possible?

struct MyType <: SomeAbstractType
    field1
    field2
    field3
    other::Dict
end

function MyType(d::Dict{AbstractString,AbstractString})
    var1 = f(d, "field1")
    var2 = f(d, "field2")
    var3 = f(d, "field3")

    MyType(var1, var2, var3, d)
end

function meta_constructor(d::Dict{AbstractString,AbstractString}, input::T)
     where T <: SomeAbstractType

    mytuple = for fields in fieldnames(T) ...

    T(mytuple)
end
2

Yes, that is possible. However, if you’re constructing from a dict, which will be type-unstable and not super performant, I don’t see a need to do it. I don’t think you gain anything from your current solution.

3

A lot of lines actually … roughly 1k … and I am a bit lazy

4

Does this not work:

function meta_constructor(d::Dict{AbstractString,AbstractString}, input::T)
     where T <: SomeAbstractType
    T((d[string(fld)] for fld in fieldnames(T))...)
end

?
(not sure what the f(d, "field1") is about, but this could be added too)

5

Thanks, I’m going to try it!

6

Corrected an error in the example. Probably you’re aware of this:
Also if you use a Dict{Symbol, AbstractString} then you can drop the string conversion. Last, if you can use a Dict{Symbol, String} and uses fields field1::String, you might speed things up.