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relax dispatch for the IteratorSize method for Generator #58110

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Merged
merged 1 commit into from
May 31, 2025
Merged

relax dispatch for the IteratorSize method for Generator #58110

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2 changes: 1 addition & 1 deletion base/generator.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -98,7 +98,7 @@ IteratorSize(::Type{Any}) = SizeUnknown()

IteratorSize(::Type{<:Tuple}) = HasLength()
IteratorSize(::Type{<:AbstractArray{<:Any,N}}) where {N} = HasShape{N}()
IteratorSize(::Type{Generator{I,F}}) where {I,F} = IteratorSize(I)
IteratorSize(::Type{<:Generator{I}}) where {I} = (@isdefined I) ? IteratorSize(I) : SizeUnknown()
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Apologies for the dumb question, but in which scenario would @isdefined I return false ?

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The bottom type does it:

julia> struct S{P} end
 
julia> f(::Type{<:S}) = "fallback"
f (generic function with 1 method)
 
julia> f(::Type{<:S{P}}) where {P} = (@isdefined P) ? "is defined" : "is not defined"
f (generic function with 2 methods)
 
julia> f(Union{})
"is not defined"

@isdefined is often used like that in eltype method definitions.


haslength(iter) = IteratorSize(iter) isa Union{HasShape, HasLength}

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6 changes: 6 additions & 0 deletions test/iterators.jl
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Expand Up @@ -988,6 +988,12 @@ end
@test accumulate(+, (x^2 for x in 1:3); init=100) == [101, 105, 114]
end

@testset "issue #58109" begin
i = Iterators.map(identity, 3)
j = Iterators.map(sqrt, 7)
@test (@inferred Base.IteratorSize(i)) === @inferred Base.IteratorSize(eltype([i, j]))
end

@testset "IteratorSize trait for zip" begin
@test (@inferred Base.IteratorSize(zip())) == Base.IsInfinite() # for zip of empty tuple
@test (@inferred Base.IteratorSize(zip((1,2,3), repeated(0)))) == Base.HasLength() # for zip of ::HasLength and ::IsInfinite
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