define isassigned(r::Ref) = isdefined(r, :x)?

[stevengj]

It really seems like we should be able to do isdefined(r::Ref), in analogy with isdefined(a) for a zero-dimensional array (in both cases, you access the contents with []). Right now, you have to do isdefined(r, :x), which is annoying because it depends on the internal implementation of RefValue.

Unfortunately, it's not as simple as Base.isdefined(r::Ref) = isdefined(r, :x) because isdefined is a builtin. Maybe Core.isdefined should be the builtin, and Base.isdefined should be a generic function that wraps around Core.isdefined?

(This came up in JuliaLang/IJulia.jl#447, cc @malmaud)

[malmaud]

I agree this would be the best, but it might also be reasonable to use isassigned for this purpose, #18082.

[yuyichao]

Closed by #18082