Silly POC of OO-style instance methods in Julia

oo.jl

tablename(x::Symbol) = Symbol(:methtab_, x)

macro instancemethod(T::Symbol, ex::Expr)
    @assert ex.head ∈ (:function, :(=))
    table = tablename(T)
    name = ex.args[1].args[1]
    insert!(ex.args[1].args, 2, :(this::$T))
    quote
        $(esc(ex))
        $table[$(QuoteNode(name))] = $name
    end
end

macro OO(ex::Expr)
    @assert ex.head === :struct
    T = ex.args[2]
    table = esc(tablename(T))
    quote
        const $table = Dict{Symbol, Function}()
        $(esc(ex))
        function Base.getproperty(x::$T, name::Symbol)
            return if haskey($table, name)
                (args...; kwargs...) -> $table[name](x, args...; kwargs...)
            else
                getfield(x, name)
            end
        end
    end
end

@OO mutable struct Foo
    x::Int
end

@instancemethod Foo set_x(x::Int) = this.x = x

f = Foo(1)
f.set_x(10)
@show f