Add 'isassigned' for RefValue

[malmaud]

Useful to avoid the need for users to break encapsulation by directly referencing the fields of RefValue

[stevengj]

I would strongly prefer isdefined as in #18086, in analogy with Array.

[yuyichao]

We already have isassigned why not just use it? isdefined as a builtin has a well defined meaning and shouldn't be overloaded.

[stevengj]

@yuyichao, I'd rather get rid of isassigned entirely, as having both isdefined(array, i) and isassigned(array, i) with almost identical meanings seems odd and confusing to me.

The fact that isdefined is a builtin seems like an implementation detail. We can make Core.isdefined the builtin and have Base.isdefined be a generic-function wrapper.

[yuyichao]

isdefined(array, i) is an implementation detail of isassigned(array, i) and will be gone after #12447 so isassigned(array, i) should always be used instead of isdefined(array, i).

More importantly for certain types (AbstractArrays for example) isdefined and isassigned are both meaningful and have non-compatible meanings so we can't have a single generic function wrapper for them and must have two functions (i.e. isdefined and isassigned).

[stevengj]

In what case should isassigned(array, i) give a different result from isdefined(array, i)? I don't understand the problem you suggest with AbstractArray.

(There are plenty of cases where isdefined does not currently work because it is an intrinsic, but that is an implementation detail. The question is, why do we have two names for basically the same operation?)

[yuyichao]

In what case should isassigned(array, i) give a different result from isdefined(array, i)

Yes. (Assuming you mean array::Array) The special case for array will be gone and isdefined(array, i) will return if the ith field of the new array object is defined or not. Note that this is already the case for some AbstractArray objects, which is the problem I suggested with AbstractArray.

julia> isdefined(view(Vector{Any}(3), :), 1)
true

julia> isassigned(view(Vector{Any}(3), :), 1)
false

The question is, why do we have two names for basically the same operation?

isdefined is used to determine if a field of an object is defined. isassigned is used to determine if a key of a container is defined.

[yuyichao]

isdefined is used to determine if a field of an object is defined. isassigned is used to determine if a key of a container is defined.

i.e. they are not the same operation at all. It is unfortunate that isassigned for Array is implemented using the isdefined builtin, it would have been better if we use an arrayassigned intrinsic for that instead. Oh well.

[stevengj]

Okay, looks like the consensus is for isassigned. Restarting Travis since the timeout error seems unrelated.

[kshyatt]

CI passed but looks like we still need tests?

[malmaud]

@kshyatt Which test file does this belong in?

[malmaud]

Tests added

[kshyatt]

Not sure, to be honest. Maybe whichever file(s) the ccall tests are in?

[malmaud]

Good to merge?

[tkelman]

Not worth creating a new test file and the printing and process spawning overhead of that for such a small nunber of new tests. ccall seems like a decent enough place for them, or misc

[malmaud]

@tkelman Done