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Fixing abs for Rational{<:Unsigned} #29561

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merged 5 commits into from
Oct 9, 2018
Merged

Fixing abs for Rational{<:Unsigned} #29561

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0e8abd4
Fix abs for Rational{<:Unsigned}
lcontento Oct 8, 2018
3d9ad10
Add tests for abs(x::Rational)
lcontento Oct 8, 2018
ffacc18
Remove extra white space in test/rational.jl
lcontento Oct 8, 2018
8d7c863
Add PR reference
lcontento Oct 9, 2018
3e391fa
Update rational.jl
lcontento Oct 9, 2018
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Fix abs for Rational{<:Unsigned}
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@lcontento
lcontento authored Oct 8, 2018
commit 0e8abd4592ecd7e214071cf29a9e5d94c97d6b25
2 changes: 2 additions & 0 deletions base/rational.jl
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Expand Up @@ -226,6 +226,8 @@ signbit(x::Rational) = signbit(x.num)
copysign(x::Rational, y::Real) = copysign(x.num,y) // x.den
copysign(x::Rational, y::Rational) = copysign(x.num,y.num) // x.den

abs(x::Rational{T}) where {T<:Unsigned} = x
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An alternative approach (and maybe more general?) would be to define

abs(x::Rational) = Rational(abs(x.num), x.den)

but I don't know what is best.
I also wonder if the ifelse in numbers.jl could simply be a ternary, i.e.

abs(x::Real) = signbit(x) ? -x : x

since, as noted in this PR, not all numbers can be negated.

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When T is unsigned, it is true that the ratio cannot be negative, so I guess this is fine. It's a bit weird to be using unsigned integers for rationals in the first place though, isn't it? I do think that @fredrikekre's suggestion for a generic definition that works for all rationals by calling abs on the numerator is better.

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Indeed @fredrikekre's proposal appears to be more general. Should I add another commit to the same PR making the change or resubmit a cleaner one?

By the way, I was using unsigned rationals since it is a possible tag type for EXIF metadata. I agree that they are a strange choice in a general use case.

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Just add more commits here. Much easier that way. We can squash it when it’s ready.


typemin(::Type{Rational{T}}) where {T<:Integer} = -one(T)//zero(T)
typemax(::Type{Rational{T}}) where {T<:Integer} = one(T)//zero(T)

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