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last(itr) should use Iterators.reverse #43497

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last(itr) should use Iterators.reverse #43497

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1ba8d7d
last(itr) should use Iterators.reverse
stevengj Dec 20, 2021
bca63f1
doc fix
stevengj Dec 20, 2021
c819079
Cmd fix
stevengj Dec 20, 2021
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12 changes: 7 additions & 5 deletions base/abstractarray.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -459,11 +459,12 @@ function first(v::AbstractVector, n::Integer)
end

"""
last(coll)
last(itr)

Get the last element of an ordered collection, if it can be computed in O(1) time. This is
accomplished by calling [`lastindex`](@ref) to get the last index. Return the end
point of an [`AbstractRange`](@ref) even if it is empty.
Get the last element of an ordered collection `itr`, if it can be computed
in O(1) time. This is accomplished for general iterable collections by
calling [`first`](@ref) on [`Iterators.reverse(itr)`](@ref Iterators.reverse).
(Returns the end point of an [`AbstractRange`](@ref) even if it is empty.)

See also [`first`](@ref), [`endswith`](@ref).

Expand All @@ -476,7 +477,8 @@ julia> last([1; 2; 3; 4])
4
```
"""
last(a) = a[end]
last(a) = first(Iterators.reverse(itr))
last(a::Union{AbstractArray,Tuple,Cmd}) = a[end]

"""
last(itr, n::Integer)
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3 changes: 0 additions & 3 deletions base/io.jl
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Expand Up @@ -1167,9 +1167,6 @@ end
isdone(r::Iterators.Reverse{<:EachLine}, state) = isempty(state.chunks)
isdone(r::Iterators.Reverse{<:EachLine}) = isdone(r.itr)

# use reverse iteration to get end of EachLines (if possible)
last(itr::EachLine) = first(Iterators.reverse(itr))

struct ReadEachIterator{T, IOT <: IO}
stream::IOT
end
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