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Allow Iterators.flatten for empty tuple #29112

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Sep 12, 2018
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Allow Iterators.flatten for empty tuple #29112

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046be32
allow Iterators.flatten for empty tuple
KlausC Sep 10, 2018
61f1256
added testcase for `Iterators.flatten(())`
KlausC Sep 10, 2018
fcbea5f
moved method of `IteratorEltype` to `generator.jl`
KlausC Sep 11, 2018
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2 changes: 2 additions & 0 deletions base/iterators.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -873,13 +873,15 @@ julia> collect(Iterators.flatten((1:2, 8:9)))
flatten(itr) = Flatten(itr)

eltype(::Type{Flatten{I}}) where {I} = eltype(eltype(I))
IteratorEltype(::Type{Union{}}) = EltypeUnknown()
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This can go in generator.jl along with the other standard methods for IteratorEltype; it's not specific to flatten.

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ok - I will move the line to generator.jl

IteratorEltype(::Type{Flatten{I}}) where {I} = _flatteneltype(I, IteratorEltype(I))
_flatteneltype(I, ::HasEltype) = IteratorEltype(eltype(I))
_flatteneltype(I, et) = EltypeUnknown()

flatten_iteratorsize(::Union{HasShape, HasLength}, ::Type{<:NTuple{N,Any}}) where {N} = HasLength()
flatten_iteratorsize(::Union{HasShape, HasLength}, ::Type{<:Tuple}) = SizeUnknown()
flatten_iteratorsize(::Union{HasShape, HasLength}, ::Type{<:Number}) = HasLength()
flatten_iteratorsize(::Union{HasShape, HasLength}, ::Type{Union{}}) = SizeUnknown()
flatten_iteratorsize(a, b) = SizeUnknown()

_flatten_iteratorsize(sz, ::EltypeUnknown, I) = SizeUnknown()
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1 change: 1 addition & 0 deletions test/iterators.jl
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Expand Up @@ -365,6 +365,7 @@ end
@test length(flatten(zip(1:3, 4:6))) == 6
@test length(flatten(1:6)) == 6
@test collect(flatten(Any[])) == Any[]
@test collect(flatten(())) == Union{}[]
@test_throws ArgumentError length(flatten(NTuple[(1,), ()])) # #16680
@test_throws ArgumentError length(flatten([[1], [1]]))

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