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zero(Quantity{Int64, D, U} where U where D) should error? #264

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goretkin opened this issue Aug 28, 2019 · 1 comment · Fixed by #266
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zero(Quantity{Int64, D, U} where U where D) should error? #264

goretkin opened this issue Aug 28, 2019 · 1 comment · Fixed by #266

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@goretkin
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goretkin commented Aug 28, 2019 •
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julia> zero(Quantity{Int64, D, U} where U where D)
0

This happens via a fallback to

julia> convert(Quantity{Int64, D, U} where U where D, 0)
0

The convert behavior makes sense, since it returns a representation of 0 of type Quantity{Int64, D, U} where U where D. But I'm not sure what it means to return the zero element of a quantity whose units are not specified.

I came to this conclusion via JuliaLang/julia#33099 which, in my opinion, erroneously succeeds and should have instead failed under the fallback for zero.
ajkeller34 pushed a commit to rigetti/Unitful.jl that referenced this issue Sep 1, 2019
Clarify the behavior of zero on Quantity types that are not fully…
f4da250 
… specified. Closes PainterQubits#264.

- `zero(::Type{<:AbstractQuantity{T}}) where T` should fail.
- `zero(::Type{<:AbstractQuantity{T,D}}) where {T,D}` should use `upreferred(D)`.
@ajkeller34 ajkeller34 mentioned this issue Sep 1, 2019
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@ajkeller34
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I think this should be fixed now—I also implemented behavior for types like Quantity{Int64, 𝐋}.

@ChrisRackauckas ChrisRackauckas mentioned this issue Sep 8, 2019
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Clarify the behavior of zero on Quantity types… rigetti/Unitful.jl
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@goretkin @ajkeller34