setindex!! turns an OrderedDict to a Dict

[mhauru]

julia> typeof(setindex!!(OrderedDict{Union{},Union{}}(), 0, 4))
Dict{Int64, Int64}

This only happens if the key or element type needs widening. Not sure what the solution here is. Maybe OrderedCollections needs a BangBang extension?

Later...

Just tried to understand this a bit better, and the culprit method is this, which reads

function _setindex(d0::AbstractDict, v, k)
    K = promote_type(keytype(d0), typeof(k))
    V = promote_type(valtype(d0), typeof(v))
    d = Dict{K, V}()
    copy!(d, d0)
    d[k] = v
    return d
end

This feels quite funny to me: Any AbstractDict, under non-mutating _setindex, is just straight-up changed to a Dict.

What's the interface that every AbstractDict type must implement? Is it documented somewhere? I can't find it.

If it includes merge, and it might, then we could do

function _setindex(d0::AbstractDict, v, k)
    return merge(d0, basetypeof(d0)(k => v))
end

where basetypeof gets the type of d0 stripped of type parameters (I forget now how to do it).

Or we could do something like

function _setindex(d0::AbstractDict, v, k)
    K = promote_type(keytype(d0), typeof(k))
    V = promote_type(valtype(d0), typeof(v))
    d = basetypeof(d0){K,V}(k => v)
    for k0, v0 in items(d0)
        d[k0] = v0
    end
    return d
end

although I'm not sure what basetypeof(d0){K,V} there means, because even though every AbstractDict type must have a K and V type parameter, they don't need to be the first two type parameters.

[CameronBieganek]

What's the interface that every AbstractDict type must implement? Is it documented somewhere? I can't find it.

Unfortunately there is no explicitly documented interface for AbstractDict.

where basetypeof gets the type of d0 stripped of type parameters (I forget now how to do it).

I don't think there's a public way to do that, for better or worse.

basetypeof(d0){K,V}(k => v)

Even if we knew what the interface for AbstractDict was, it probably wouldn't include a specification for the constructors of AbstractDicts. Constructors are usually not included in the interface for an abstract type, since they can be so different depending on the concrete type.

Anyhow, I think we could use the three argument version of empty, something like this:

function _setindex(d0::AbstractDict, v, k)
    K = promote_type(keytype(d0), typeof(k))
    V = promote_type(valtype(d0), typeof(v))
    d = empty(d0, K, V)
    copy!(d, d0)
    d[k] = v
    return d
end