How to document type properties defined with `getproperty`?

General Usage
1

Consider the structs Foo and Bar:

"""
Doc for type `Foo`.
"""
struct Foo
  """
  Doc for field Foo.x
  """
  x::Int
  Foo() = new(2)
end

"""
Doc for type `Bar`.
"""
struct Bar end

Base.propertynames(::Bar) = (:x,)

function Base.getproperty(a::Bar,s::Symbol)
  if s == :x
    2
  else
    error("type Bar has no field $s")
  end
end

function Base.show(io::IO,::Bar)
  print(io,"Bar(2)")
end

They have an (almost) identical API

julia> foo = Foo()
Foo(2)

julia> bar = Bar()
Bar(2)

julia> foo.x
2

julia> bar.x
2

Except for documentation

help?> Foo.x
  Doc for field Foo.x

help?> Bar.x
  Bar has no fields.

Is there any way of documenting the property Bar.x ?

Thanks for the help!

2

This is currently an open question, and there is no solution for it that would replicate the convenience of the field docstring. Cf

https://github.com/JuliaLang/julia/issues/27119

I would suggest documenting valid properties in the docstring of Foo, or the usual function that users call to make Foo.

1 Like
3

Thanks for answering!

Another solution I can think of is to create a getter getx(a::Bar) = a.x and document this getter and inform the users of the package that properties are documented in the corresponding getter.

Do you see any problem with this?

4

If there is an explicit accessor function, it is of course good practice to document that.

But one advantage of property accessors is that you don’t have to bother with defining a function for this. How to document that is somewhat of an open question while practice evolves, but at least discoverability is fine thanks to propertynames.

2 Likes