Comments (8)
vtjnash
commented on May 24, 2024
1
_myuniontypes relies upon an implementation bug in subtyping and should be avoided in real code
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mikmoore
commented on May 24, 2024
I think something like the current Base.uniontypes that specializes and returns a Tuple (rather than current @nospecialize-annotated function returning a Vector{Any}, which is mostly used for codegen and tests) could fit this bill.
I would even consider commandeering this function name for this purpose and replacing the internal one with something else (where it matters -- I'm sure letting it specialize in some places wouldn't be catastrophic).
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vtjnash
commented on May 24, 2024
Such as Base.uniontypes? Note that it is pretty tricky to work with the structure of a Union correctly, since its fields are not a independent collection in themselves, but rather only when taken as a whole (e.g. the problems with #48205)
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vtjnash
commented on May 24, 2024
If Base.uniontypes returned a Tuple, it would not be inferable concretely, which seems like a massive footgun (#48205).
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mikmoore
commented on May 24, 2024
I don't think I properly understand the entire issue with concrete inferability. But I see the linked issue and how the difficulty of canonicalizing Unions can cause trouble, as well as the complication of shared typevars within a Union.
In any case, the following definition appears to only use external properties (plus the implementation detail that Unions of more than two types are made by nesting)
# ::Type overwrites ::Type{Union{...}}, so we need two different functions here
myuniontypes(x::Type) = (x,)
myuniontypes(x::Union) = _myuniontypes(x)
_myuniontypes(::Type{Union{A,B}}) where {A,B} = (myuniontypes(A)...,myuniontypes(B)...)with the results
julia> myuniontypes(Base.IEEEFloat)
(Float16, Float32, Float64)
julia> @code_warntype myuniontypes(Base.IEEEFloat) # properly inferred as a constant
MethodInstance for myuniontypes(::Type{Union{Float16, Float32, Float64}})
from myuniontypes(x::Union) @ Main REPL[2]:1
Arguments
#self#::Core.Const(myuniontypes)
x::Type{Union{Float16, Float32, Float64}}
Body::Tuple{DataType, DataType, DataType}
1 ─ %1 = Main._myuniontypes(x)::Core.Const((Float16, Float32, Float64))
└── return %1
julia> myuniontypes(AbstractVecOrMat{Float64})
(AbstractVector{Float64}, AbstractMatrix{Float64})
julia> myuniontypes(AbstractVecOrMat{<:Real}) # can't reduce due to shared typevar
(AbstractVecOrMat{<:Real},)
julia> myuniontypes(Union{AbstractVector{<:Real},AbstractMatrix{<:Real}}) # distinct typevars
(AbstractVector{<:Real}, AbstractMatrix{<:Real})
julia> myuniontypes(StridedMatrix{Float64}) # actually comes out better than I would have expected
( # added line breaks for "readability"
DenseMatrix{Float64},
Base.ReinterpretArray{Float64, 2, S, A, IsReshaped} where {A<:Union{SubArray{T, N, A, I, true} where {T, N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray}, IsReshaped, S},
Base.ReshapedArray{Float64, 2, A} where A<:Union{Base.ReinterpretArray{T, N, S, A, IsReshaped} where {T, N, A<:Union{SubArray{T, N, A, I, true} where {T, N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray}, IsReshaped, S}, SubArray{T, N, A, I, true} where {T, N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray},
SubArray{Float64, 2, A, I} where {A<:Union{Base.ReinterpretArray{T, N, S, A, IsReshaped} where {T, N, A<:Union{SubArray{T, N, A, I, true} where {T, N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray}, IsReshaped, S}, Base.ReshapedArray{T, N, A} where {T, N, A<:Union{Base.ReinterpretArray{T, N, S, A, IsReshaped} where {T, N, A<:Union{SubArray{T, N, A, I, true} where {T, N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray}, IsReshaped, S}, SubArray{T, N, A, I, true} where {T, N, A<:DenseArray, I<:Union{Tuple{Vararg{Real}}, Tuple{AbstractUnitRange, Vararg{Any}}}}, DenseArray}}, DenseArray}, I<:Tuple{Vararg{Union{Base.AbstractCartesianIndex, AbstractRange{<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}}, Base.ReshapedArray{T, N, A, Tuple{}} where {T, N, A<:AbstractUnitRange}, Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}}}}
)
There certainly are situations where a more specific answer doesn't exist (and maybe this function should be made to throw errors for those). But for "simple" results this appears to work. Is this the sort of implementation we should be directing people to for questions like this one? One could say this is still no better than internals like Base.uniontypes because it depends on the "nested binary unions" implementation detail. I can't say I love it for code outside of Base, but we need some kind of answer for these questions.
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Tokazama
commented on May 24, 2024
Such as
Base.uniontypes? Note that it is pretty tricky to work with the structure of a Union correctly, since its fields are not a independent collection in themselves, but rather only when taken as a whole (e.g. the problems with #48205)
This is why we should have something like Base.uniontypes, to discourage people from mucking around with internals that may change in the future or are tricky to get right. Right now people just directly access the the fields of Union and iterate over it like a list.
If
Base.uniontypesreturned a Tuple, it would not be inferable concretely, which seems like a massive footgun (#48205).
Couldn't we just return a tuple of types instead of a Tuple type?
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vtjnash
commented on May 24, 2024
neither big or little t Tuple is inferable because of how the type system works (#48205)
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Tokazama
commented on May 24, 2024
The union_to_tuple function below manually unrolls into a tuple up to length of 32. If the union is longer than that it pushes to a locally created vector then collects into a tuple.
In the most naive case where we only know we're working with Union this infers Tuple. If the union type is being lowered from some other type parameter, then we can completely infer everything (e.g., eltype_variants(::Type{<:Array{T}}) where {T} = isa(T, Union) ? union_to_tuple(T) : T will know the exact return type). I think this gets us to the same level of inference as fieldtypes.
implementation of `union_to_tuple`
function union_to_tuple(b0::Union)
(a1 = getfield(b0, 1); b1 = getfield(b0, 2); isa(b1, Union)) || return (a1, b1)
(a2 = getfield(b1, 1); b2 = getfield(b1, 2); isa(b2, Union)) || return (a1, a2, b2)
(a3 = getfield(b2, 1); b3 = getfield(b2, 2); isa(b3, Union)) || return (a1, a2, a3, b3)
(a4 = getfield(b3, 1); b4 = getfield(b3, 2); isa(b4, Union)) || return (a1, a2, a3, a4, b4)
(a5 = getfield(b4, 1); b5 = getfield(b4, 2); isa(b5, Union)) || return (a1, a2, a3, a4, a5, b5)
(a6 = getfield(b5, 1); b6 = getfield(b5, 2); isa(b6, Union)) || return (
a1, a2, a3, a4, a5, a6, b6
)
(a7 = getfield(b6, 1); b7 = getfield(b6, 2); isa(b7, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, b7
)
(a8 = getfield(b7, 1); b8 = getfield(b7, 2); isa(b8, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, b8
)
(a9 = getfield(b8, 1); b9 = getfield(b8, 2); isa(b9, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, b9
)
(a10 = getfield(b9, 1); b10 = getfield(b9, 2); isa(b10, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, b10
)
(a11 = getfield(b10, 1); b11 = getfield(b10, 2); isa(b11, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, b11
)
(a12 = getfield(b11, 1); b12 = getfield(b11, 2); isa(b12, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, b12
)
(a13 = getfield(b12, 1); b13 = getfield(b12, 2); isa(b13, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, b13
)
(a14 = getfield(b13, 1); b14 = getfield(b13, 2); isa(b14, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, b14
)
(a15 = getfield(b14, 1); b15 = getfield(b14, 2); isa(b15, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, b15
)
(a16 = getfield(b15, 1); b16 = getfield(b15, 2); isa(b16, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, b16
)
(a17 = getfield(b16, 1); b17 = getfield(b16, 2); isa(b17, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, b17
)
(a18 = getfield(b17, 1); b18 = getfield(b17, 2); isa(b18, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
b18
)
(a19 = getfield(b18, 1); b19 = getfield(b18, 2); isa(b19, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, b19
)
(a20 = getfield(b19, 1); b20 = getfield(b19, 2); isa(b20, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, b20
)
(a21 = getfield(b20, 1); b21 = getfield(b20, 2); isa(b21, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, b21
)
(a22 = getfield(b21, 1); b22 = getfield(b21, 2); isa(b22, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, b22
)
(a23 = getfield(b22, 1); b23 = getfield(b22, 2); isa(b23, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, b23
)
(a24 = getfield(b23, 1); b24 = getfield(b23, 2); isa(b24, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, b24
)
(a25 = getfield(b24, 1); b25 = getfield(b24, 2); isa(b25, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, b25
)
(a26 = getfield(b25, 1); b26 = getfield(b25, 2); isa(b26, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, a26, b26
)
(a27 = getfield(b26, 1); b27 = getfield(b26, 2); isa(b27, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, a26, a27, b27
)
(a28 = getfield(b27, 1); b28 = getfield(b27, 2); isa(b28, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, b28
)
(a29 = getfield(b28, 1); b29 = getfield(b28, 2); isa(b29, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, b29
)
(a30 = getfield(b29, 1); b30 = getfield(b29, 2); isa(b30, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, b30
)
(a31 = getfield(b30, 1); b31 = getfield(b30, 2); isa(b31, Union)) || return (
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, a31, b31
)
uvec = [
a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, a31
]
utail = b31
while true
push!(uvec, getfield(utail, 1))
tmp = getfield(utail, 2)
if isa(tmp, Union)
utail = tmp
else
push!(uvec, tmp)
break
end
end
return Tuple(uvec)
endfrom julia.
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