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Allow empty reductions for maximum(Unsigned) and compose #44702

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Allow empty reductions for maximum(Unsigned) and compose #44702

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24add19
Allow empty reductions for maximum(Unsigned) and compose
eschnett Mar 22, 2022
f5c0a67
Correct error
eschnett Mar 23, 2022
1a68da6
Correct error
eschnett Mar 23, 2022
bd16143
Correct reduce_empty for maximum
eschnett Mar 23, 2022
30df7fb
Correct reduce_empty for maximum
eschnett Mar 23, 2022
2ea73c1
Correct output in documentation for maximum
eschnett Mar 23, 2022
7469597
Update tests for error messages
eschnett Mar 23, 2022
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8 changes: 7 additions & 1 deletion base/reduce.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -347,6 +347,8 @@ reduce_empty(::typeof(*), ::Type{T}) where {T} = one(T)
reduce_empty(::typeof(*), ::Type{<:AbstractChar}) = ""
reduce_empty(::typeof(&), ::Type{Bool}) = true
reduce_empty(::typeof(|), ::Type{Bool}) = false
reduce_empty(::typeof(∘), ::Type{Union{}}) = _empty_reduce_error(∘, Union{})
reduce_empty(::typeof(∘), ::Type) = identity

reduce_empty(::typeof(add_sum), ::Type{Union{}}) = _empty_reduce_error(add_sum, Union{})
reduce_empty(::typeof(add_sum), ::Type{T}) where {T} = reduce_empty(+, T)
Expand All @@ -356,6 +358,9 @@ reduce_empty(::typeof(mul_prod), ::Type{Union{}}) = _empty_reduce_error(mul_prod
reduce_empty(::typeof(mul_prod), ::Type{T}) where {T} = reduce_empty(*, T)
reduce_empty(::typeof(mul_prod), ::Type{T}) where {T<:SmallSigned} = one(Int)
reduce_empty(::typeof(mul_prod), ::Type{T}) where {T<:SmallUnsigned} = one(UInt)
reduce_empty(::typeof(max), ::Type{T}) where {T} = _empty_reduce_error(maximum, T)
reduce_empty(::typeof(max), ::Type{T}) where {T<:Unsigned} = zero(T)
reduce_empty(::typeof(max), ::Type{Union{}}) = _empty_reduce_error(maximum, Union{})

reduce_empty(op::BottomRF, ::Type{T}) where {T} = reduce_empty(op.rf, T)
reduce_empty(op::MappingRF, ::Type{T}) where {T} = mapreduce_empty(op.f, op.rf, T)
Expand Down Expand Up @@ -753,7 +758,8 @@ julia> maximum([1,2,3])
3

julia> maximum(())
ERROR: MethodError: reducing over an empty collection is not allowed; consider supplying `init` to the reducer
ERROR: ArgumentError: reducing with maximum over an empty collection of element type Union{} is not allowed.
You may be able to prevent this error by supplying an `init` value to the reducer.
Stacktrace:
[...]

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7 changes: 6 additions & 1 deletion test/reduce.jl
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Expand Up @@ -53,6 +53,9 @@ end
@test reduce(max, [8 6 7 5 3 0 9]) == 9
@test reduce(+, 1:5; init=1000) == (1000 + 1 + 2 + 3 + 4 + 5)
@test reduce(+, 1) == 1
@test reduce(∘, [])(42) == 42
@test reduce(∘, [x->2x+1])(42) == 85
@test reduce(∘, [x->x*"2", x->x*"1"])("0") == "012"
@test_throws "reducing with * over an empty collection of element type Union{} is not allowed" reduce(*, ())
@test_throws "reducing with * over an empty collection of element type Union{} is not allowed" reduce(*, Union{}[])

Expand Down Expand Up @@ -248,10 +251,12 @@ prod2(itr) = invoke(prod, Tuple{Any}, itr)

# maximum & minimum & extrema

@test_throws "reducing over an empty" maximum(Int[])
@test_throws "reducing with maximum over an empty" maximum(Int[])
@test_throws "reducing over an empty" minimum(Int[])
@test_throws "reducing over an empty" extrema(Int[])

@test maximum(UInt[]) === UInt(0)

@test maximum(Int[]; init=-1) == -1
@test minimum(Int[]; init=-1) == -1
@test extrema(Int[]; init=(1, -1)) == (1, -1)
Expand Down
3 changes: 2 additions & 1 deletion test/reducedim.jl
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Expand Up @@ -184,7 +184,8 @@ end
@test prod(A) === 1
@test_throws ["reducing over an empty",
"consider supplying `init`"] minimum(A)
@test_throws "consider supplying `init`" maximum(A)
@test_throws ["reducing with maximum over an empty",
"prevent this error by supplying an `init`"] maximum(A)

@test isequal(sum(A, dims=1), zeros(Int, 1, 1))
@test isequal(sum(A, dims=2), zeros(Int, 0, 1))
Expand Down