Query Array ownership with isshared and isowner

[Tokazama]

Resizing operations throw errors on shared arrays but there's currently no way to find this out until an error is thrown. isshared lets us know before execution that an array may be shared and isowner lets us know if the array is the original owner, potentially allowing "unsharing" data. (#47537).

This recently came up alongside discussion of other traits for characterizing this information at the type level (#46500).

[Tokazama]

@Jutho, I know it's a bit late to be addressing this but thought you may be interested nonetheless

[Jutho]

Pinging @dkarrasch , who is now maintaining LinearMaps.jl where this came up.

[Tokazama]

@dkarrasch , I'm assuming that thumbs up means this is still useful?

This would also be good so we could start developing the interface for changing collection sizes. Then we could get have more generic user facing methods like

function push!(x::AbstractVector, item)
    isshared(x) || error("cannot resize array with shared data")
    unsafe_growend!(x, 1)
    unsafe_setindex!(x, item, x)
    return x
end

[dkarrasch]

In LinearMaps.jl, we have an "ugly" try-catch-block to catch cases when some vector cannot be resized. It would be nice to replace this with a specific and clear predicate.

[Tokazama]

Whose the appropriate core dev to ping to get this moving forward?

This is the sort of thing I'd like to be able to do.

[vtjnash]

This error is now gone