altre
October 10, 2019, 6:02am
#1
I’m having trouble to understand the following behavior of Iterators.Stateful. This is as expected
julia> for a in Iterators.Stateful([1,2,3])
print(a)
end
123
But this seems strange:
julia> [a for a in Iterators.Stateful([1,2,3])]
2-element Array{Int64,1}:
1
2
julia> [a for a in Iterators.Stateful([1])]
ERROR: BoundsError: attempt to access 0-element Array{Int64,1} at index [1]
Is this a bug, or is there something I don’t understand here?
Looking at the code
function collect(itr::Generator)
isz = IteratorSize(itr.iter)
et = @default_eltype(itr)
if isa(isz, SizeUnknown)
return grow_to!(Vector{et}(), itr)
else
y = iterate(itr)
if y === nothing
return _array_for(et, itr.iter, isz)
end
v1, st = y
collect_to_with_first!(_array_for(typeof(v1), itr.iter, isz), v1, itr, st)
end
end
The iterate call at
_array_for(::Type{T}, itr, ::HasLength) where {T} = Vector{T}(undef, Int(length(itr)::Integer))
_array_for(::Type{T}, itr, ::HasShape{N}) where {T,N} = similar(Array{T,N}, axes(itr))
function collect(itr::Generator)
isz = IteratorSize(itr.iter)
et = @default_eltype(itr)
if isa(isz, SizeUnknown)
return grow_to!(Vector{et}(), itr)
else
y = iterate(itr)
if y === nothing
return _array_for(et, itr.iter, isz)
end
v1, st = y
collect_to_with_first!(_array_for(typeof(v1), itr.iter, isz), v1, itr, st)
end
end
_collect(c, itr, ::EltypeUnknown, isz::SizeUnknown) =
grow_to!(_similar_for(c, @default_eltype(itr), itr, isz), itr)
makes length(itr) go from 1 to 0.
Then in _array_for(typeof(v1), itr.iter, isz):
return quote
if $I isa Generator && ($I).f isa Type
($I).f
else
Any
end
end
end
end
_array_for(::Type{T}, itr, ::HasLength) where {T} = Vector{T}(undef, Int(length(itr)::Integer))
_array_for(::Type{T}, itr, ::HasShape{N}) where {T,N} = similar(Array{T,N}, axes(itr))
function collect(itr::Generator)
isz = IteratorSize(itr.iter)
et = @default_eltype(itr)
if isa(isz, SizeUnknown)
return grow_to!(Vector{et}(), itr)
else
y = iterate(itr)
if y === nothing
a length 0 vector is allocated which is then tried to get assigned into:
function collect_to_with_first!(dest::AbstractArray, v1, itr, st)
i1 = first(LinearIndices(dest))
dest[i1] = v1
return collect_to!(dest, itr, i1+1, st)
end
I’m guessing the axis / length should be computed before the call to iterate.
That quite looks like a bug, is there issue for it on github?