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allow specializing Base.hash for enum types without overwriting method #49777

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Merged
merged 1 commit into from
May 23, 2023
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allow specializing Base.hash for enum types without overwriting method #49777

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16 changes: 14 additions & 2 deletions base/Enums.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,14 @@ Base.cconvert(::Type{T}, x::Enum{T2}) where {T<:Integer,T2<:Integer} = T(x)::T
Base.write(io::IO, x::Enum{T}) where {T<:Integer} = write(io, T(x))
Base.read(io::IO, ::Type{T}) where {T<:Enum} = T(read(io, basetype(T)))

"""
_enum_hash(x::Enum, h::UInt)

Compute hash for an enum value `x`. This internal method will be specialized
for every enum type created through [`@enum`](@ref).
"""
_enum_hash(x::Enum, h::UInt) = hash(x, h)
Base.hash(x::Enum, h::UInt) = _enum_hash(x, h)
Comment on lines +30 to +31
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The fallback for _enum_hash has to be something else, otherwise these two methods just call each other resulting in stack overflows (fredrikekre/EnumX.jl#5).

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@stev47 stev47 May 24, 2023 •
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Indeed, the assumption was that using @enum would create specialized hash functions to dispatch to.
This should fix it:

Suggested change
_enum_hash(x::Enum, h::UInt) = hash(x, h)
Base.hash(x::Enum, h::UInt) = _enum_hash(x, h)
_enum_hash(x::Enum, h::UInt) = invoke(hash, Tuple{Any, UInt}, x, h)
Base.hash(x::Enum, h::UInt) = _enum_hash(x, h)

Could you test and open a pull request?

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I guess I can when I find the time, but I am not the one who caused this so it is more tempting for me to press the revert button.

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opened #49964

Base.isless(x::T, y::T) where {T<:Enum} = isless(basetype(T)(x), basetype(T)(y))

Base.Symbol(x::Enum) = namemap(typeof(x))[Integer(x)]::Symbol
Expand Down Expand Up @@ -206,8 +214,12 @@ macro enum(T::Union{Symbol,Expr}, syms...)
Enums.namemap(::Type{$(esc(typename))}) = $(esc(namemap))
Base.typemin(x::Type{$(esc(typename))}) = $(esc(typename))($lo)
Base.typemax(x::Type{$(esc(typename))}) = $(esc(typename))($hi)
let enum_hash = hash($(esc(typename)))
Base.hash(x::$(esc(typename)), h::UInt) = hash(enum_hash, hash(Integer(x), h))
let type_hash = hash($(esc(typename)))
# Use internal `_enum_hash` to allow users to specialize
# `Base.hash` for their own enum types without overwriting the
# method we would define here. This avoids a warning for
# precompilation.
Enums._enum_hash(x::$(esc(typename)), h::UInt) = hash(type_hash, hash(Integer(x), h))
end
let insts = (Any[ $(esc(typename))(v) for v in $values ]...,)
Base.instances(::Type{$(esc(typename))}) = insts
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5 changes: 5 additions & 0 deletions test/enums.jl
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Expand Up @@ -179,6 +179,11 @@ end
@enum HashEnum2 Enum2_a=1
@test hash(Enum1_a) != hash(Enum2_a)

# PR #49777: Check that `Base.hash` can be specialized by the user without
# overwriting a method definition.
@enum HashEnum3 Enum3_a=1
@test which(hash, (HashEnum3, UInt)).sig != Tuple{typeof(hash), HashEnum3, UInt64}

@test (Vector{Fruit}(undef, 3) .= apple) == [apple, apple, apple]

# long, discongruous
Expand Down