Type-unstable similar and copy

[cdsousa]

For example, doing code_warntype(copy, (Images.Image{Float64,2,Array{Float64,2}},)), yields an abstract ::Images.Image{T,N,A<:AbstractArray{T,N}} return type.

This also happens with the similar method, and seems to be due to a type-unstable Image constructor.

[cdsousa]

I've around this and it seems the type-unstability resumes to line https://github.com/timholy/Images.jl/blob/master/src/core.jl#L14 ,
and more concretely to the ndims return value which, unlike eltype and typeof, doesn't allow full type inference of the new Image object...

[cdsousa]

And this seems to be an upstream issue:

type X{T}; end
f(x) = X{ndims(x)}()
code_warntype(f, (Array{Int,2},))

returns

Variables:
  x::Array{Int64,2}

Body:
  begin  # none, line 1:
      return call((top(apply_type))(Main.X,2)::Type{_<:X{T}})::X{T}
  end::X{T}

Does anyone knows if this is something already discussed in Julia list or issues?

[timholy]

It's due to this:

julia> @inferred(deepcopy(img.properties))
ERROR: return type Dict{ASCIIString,Any} does not match inferred return type Any
 in error at ./error.jl:21

which is used in Images' copy function. We use it because of this:

julia> p = Dict{ASCIIString,Any}("Hi" => rand(2,2))
Dict{ASCIIString,Any} with 1 entry:
  "Hi" => 2x2 Array{Float64,2}:…

julia> pointer(p["Hi"])
Ptr{Float64} @0x00007fbccb82b760

julia> pc = copy(p)
Dict{ASCIIString,Any} with 1 entry:
  "Hi" => 2x2 Array{Float64,2}:…

julia> pointer(pc["Hi"])
Ptr{Float64} @0x00007fbccb82b760

[timholy]

JuliaLang/julia#13323

[cdsousa]

There may be different causes for the issue at each method. For the similar method the problem is in the Image constructor (#356 (comment)) due to the unstability of ndims which suffers from an inference bug already reported: JuliaLang/julia#13082.

There is a workaround for that, and I should have already proposed a PR:
Replacing line https://github.com/timholy/Images.jl/blob/master/src/core.jl#L14
with

Image{T,N}(data::AbstractArray{T,N}, props::Dict) = Image{eltype(data),N,typeof(data)}(data,props)

will fix similar method (and probably other methods too).