Accessing public class variables

[snirgaz]

Is it possible to access public class variables without manually writing get and set methods?
For reference -- ".def_readwrite" in pybind11 allows using the "dot" syntax "A.a".

[barche]

Not yet, but this is begging to be exploited here I think: JuliaLang/julia#24960

Unfortunately I won't have time soon to get to this.

[snirgaz]

Given the v1.0 release, is the above possible?
It would greatly help my code :)

Thanks!

Snir

[barche]

No, although CxxWrap should be fully compatible with 1.0 now, this is a new feature and I haven't implemented it yet. I did think a bit on how it might be implemented, though:

• On the C++ side, add a function add_field that takes a fieldname, getter function and optional setter function. This will create Julia method called __cxxwrap_get_fieldname where fieldname is replaced by whatever the name of the field is.
• In CxxWrap, overload getproperty and setproperty! to call the named function, if it exists

That way, fields can be added without actually duplicating them on the Julia side, and it doesn't matter if getter or setter methods exist, since if they don't exist a lambda can be used to define them.

[archit120]

Are there any plans to implement this now?

[colinxs]

Another +1 here. I'm finding I have to write a lot of boilerplate code for get/set methods.

[colinxs]

Here's a solution for the Julia half:

macro wrapaccessors(T, fields)
    @assert fields.head === :tuple

    gen_case(i) = :(name === $(QuoteNode(fields.args[i])))
    gen_get(i) = quote
        $(__module__).$(Symbol(T, :_get_, fields.args[i]))(x)
    end
    gen_set(i) = quote
        $(__module__).$(Symbol(T, :_set_, fields.args[i]))(x, value)
    end

    # err_ex = :(error($(Expr(:string, "type $T has no field ", :name))))
    get_ex = Expr(:block, :($Base.getfield(x, name)))
    set_ex = Expr(:block, :($Base.setfield(x, name, value)))
    for i=2:length(fields.args)
        get_ex = Expr(:elseif, gen_case(i), gen_get(i), get_ex)
        set_ex = Expr(:elseif, gen_case(i), gen_set(i), set_ex)
    end
    get_ex = Expr(:if, gen_case(1), gen_get(1), get_ex)
    set_ex = Expr(:if, gen_case(1), gen_set(1), set_ex)

    ex = quote
        function $Base.getproperty(x::$(__module__).$(T), name::$Symbol)
            $get_ex
        end
        function $Base.setproperty!(x::$(__module__).$(T), name::$Symbol, value)
            $set_ex
        end
    end
    esc(ex)
end

# Example:
module M
    using ..Main: @wrapaccessors
    using MacroTools
    one = 0
    two = 0
    struct Example end
    Example_get_val(x::Example) = one
    Example_set_val(x::Example, v) = global one = v
    println(prettify(@macroexpand @wrapaccessors Example (one, )))
    @wrapaccessors Example (one, )
end
x = Example()
@assert x.one == M.one == 0
x.one == 10
@assert x.one == M.one == 10

I'm not familiar enough with C++ & CxxWrap's internals to come up with an elegant solution for the C++ side. But maybe someone else is? :)