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re-allow implicit prevfloat for signed step sizes #59836

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re-allow implicit prevfloat for signed step sizes #59836

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0625742
re-allow implicit `prevfloat` for signed step sizes
adienes Oct 14, 2025
9e39329
fix whitespace
adienes Oct 14, 2025
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4 changes: 4 additions & 0 deletions base/float.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -870,6 +870,10 @@ applications of [`nextfloat`](@ref) if `n < 0`.
"""
prevfloat(x::AbstractFloat, d::Integer) = _nextfloat(x, ispositive(d), uabs(d))

# this method improves backwards compatibility for types only specializing
# nextfloat and relying on an implicit prevfloat
prevfloat(x::AbstractFloat, d::T) where {T<:Signed} = nextfloat(x, -d)

"""
prevfloat(x::AbstractFloat)

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6 changes: 6 additions & 0 deletions test/floatfuncs.jl
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Expand Up @@ -316,3 +316,9 @@ end
end
end
end

@testset "nextfloat can be defined without prevfloat for signed step sizes" begin
struct MyFloat59661<:AbstractFloat x end
Base.nextfloat(x::MyFloat59661, d::Integer) = nextfloat(x.x, d)
@test prevfloat(MyFloat59661(1.0), 1) == prevfloat(1.0, 1)
end