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Fix length calculation of broadcast over tuples #23887

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Nov 7, 2017
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Fix length calculation of broadcast over tuples #23887

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27 changes: 24 additions & 3 deletions base/broadcast.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,8 @@ end
end

Base.@propagate_inbounds _broadcast_getindex(A, I) = _broadcast_getindex(containertype(A), A, I)
# `(x,)`, where `x` is a scalar, broadcasts the same way as `[x]` or `x`
Base.@propagate_inbounds _broadcast_getindex(::Type{Tuple}, A::Tuple{Any}, I) = A[1]
Base.@propagate_inbounds _broadcast_getindex(::Type{Array}, A::Ref, I) = A[]
Base.@propagate_inbounds _broadcast_getindex(::ScalarType, A, I) = A
Base.@propagate_inbounds _broadcast_getindex(::Any, A, I) = A[I]
Expand Down Expand Up @@ -333,13 +335,32 @@ end
end
@inline broadcast_c(f, ::Type{Any}, a...) = f(a...)
@inline broadcast_c(f, ::Type{Tuple}, A, Bs...) =
tuplebroadcast(f, first_tuple(A, Bs...), A, Bs...)
tuplebroadcast(f, tuplebroadcast_maxtuple(A, Bs...), A, Bs...)
@inline tuplebroadcast(f, ::NTuple{N,Any}, As...) where {N} =
ntuple(k -> f(tuplebroadcast_getargs(As, k)...), Val(N))
@inline tuplebroadcast(f, ::NTuple{N,Any}, ::Type{T}, As...) where {N,T} =
ntuple(k -> f(T, tuplebroadcast_getargs(As, k)...), Val(N))
first_tuple(A::Tuple, Bs...) = A
@inline first_tuple(A, Bs...) = first_tuple(Bs...)
# When the result of broadcast is a tuple it can only come from mixing n-tuples
# of the same length with scalars and 1-tuples. So, in order to have a
# type-stable broadcast, we need to find a tuple of maximum length (except when
# there are only scalars, empty tuples and 1-tuples, in which case the
# returned value will be an empty tuple).
# The following methods compare broadcast arguments pairwise to determine the
# length of the final tuple.
tuplebroadcast_maxtuple(A, B) =
_tuplebroadcast_maxtuple(containertype(A), containertype(B), A, B)
@inline tuplebroadcast_maxtuple(A, Bs...) =
tuplebroadcast_maxtuple(A, tuplebroadcast_maxtuple(Bs...))
tuplebroadcast_maxtuple(A::NTuple{N,Any}, ::NTuple{N,Any}...) where {N} = A
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I think this needs to be a _tuplebroadcast_maxtuple method, for example with the testcase broadcast(+, (1, 2), (3, 4), 5).

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@pabloferz pabloferz Oct 2, 2017 •
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That example works with this PR as is. I had it like this to reduce the compiler/inference work in cases where you have a bunch of tuples of the same length and a scalar element (which I imagined would be common), e.g. (1,2) .+ (2,3) .+ (3,4) .+ (4,5) .+ 1. But I can make it a _tuplebroadcast_maxtuple for consistency if preferred.

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Sorry, I screwed up the order of my example. It should be broadcast(+, 5, (1, 2), (3, 4)) which I believe would not currently work.

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@pabloferz pabloferz Nov 7, 2017 •
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I can confirm that example (or broadcast(+, (1, 2), 5, (3, 4))) works fine.

tuplebroadcast_maxtuple will call _tuplebroadcast_maxtuple only when the number of arguments to tuplebroadcast_maxtuple is two and both are not tuples of the same length (if they are, dispatch would select tuplebroadcast_maxtuple(A::NTuple{N,Any}, ::NTuple{N,Any}...) where {N} instead).

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Oh, I understand. Thanks for the correction.

# Here we use the containertype trait to easier disambiguate between methods
_tuplebroadcast_maxtuple(::Type{Any}, ::Type{Any}, A, B) = (nothing,)
_tuplebroadcast_maxtuple(::Type{Tuple}, ::Type{Any}, A, B) = A
_tuplebroadcast_maxtuple(::Type{Any}, ::Type{Tuple}, A, B) = B
_tuplebroadcast_maxtuple(::Type{Tuple}, ::Type{Tuple}, A, B::Tuple{Any}) = A
_tuplebroadcast_maxtuple(::Type{Tuple}, ::Type{Tuple}, A::Tuple{Any}, B) = B
_tuplebroadcast_maxtuple(::Type{Tuple}, ::Type{Tuple}, A::Tuple{Any}, ::Tuple{Any}) = A
_tuplebroadcast_maxtuple(::Type{Tuple}, ::Type{Tuple}, A, B) =
throw(DimensionMismatch("tuples could not be broadcast to a common size"))
tuplebroadcast_getargs(::Tuple{}, k) = ()
@inline tuplebroadcast_getargs(As, k) =
(_broadcast_getindex(first(As), k), tuplebroadcast_getargs(tail(As), k)...)
Expand Down
16 changes: 12 additions & 4 deletions test/broadcast.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -519,8 +519,16 @@ end
Nullable("hello"))
end

# Issue #21291
let t = (0, 1, 2)
o = 1
@test @inferred(broadcast(+, t, o)) == (1, 2, 3)
@testset "broadcast resulting in tuples" begin
# Issue #21291
let t = (0, 1, 2)
o = 1
@test @inferred(broadcast(+, t, o)) == (1, 2, 3)
end

# Issue #23647
@test (1, 2, 3) .+ (1,) == (1,) .+ (1, 2, 3) == (2, 3, 4)
@test (1,) .+ () == () .+ (1,) == () .+ () == ()
@test (1, 2) .+ (1, 2) == (2, 4)
@test_throws DimensionMismatch (1, 2) .+ (1, 2, 3)
end