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Clarify that the unsigned type is promoted to, if the types differ only in signedness #48973

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Mar 28, 2023
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Clarify that the unsigned type is promoted to, if the types differ only in signedness #48973

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Clarify that the unsigned type is promoted to, if the types differ on…
robertfeldt Mar 11, 2023
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fixed trailing whitespace
robertfeldt Mar 11, 2023
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updated to capture the actual behavior, which doesn't depend on the n…
robertfeldt Mar 13, 2023
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minor rewording to better follow the patter of the preceding sentence
robertfeldt Mar 13, 2023
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Merge branch 'master' into master
DilumAluthge Mar 28, 2023
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10 changes: 5 additions & 5 deletions doc/src/manual/conversion-and-promotion.md
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Expand Up @@ -233,11 +233,11 @@ julia> promote(1 + 2im, 3//4)
```

Floating-point values are promoted to the largest of the floating-point argument types. Integer
values are promoted to the larger of either the native machine word size or the largest integer
argument type. Mixtures of integers and floating-point values are promoted to a floating-point
type big enough to hold all the values. Integers mixed with rationals are promoted to rationals.
Rationals mixed with floats are promoted to floats. Complex values mixed with real values are
promoted to the appropriate kind of complex value.
values are promoted to the largest of the integer argument types. If the types are the same size
but differ in signedness, the unsigned type is chosen. Mixtures of integers and floating-point
values are promoted to a floating-point type big enough to hold all the values. Integers mixed
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@vtjnash vtjnash Mar 20, 2023 •
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The (pre-existing) floating point comment doesn't seem particularly accurate: it is just promoted to the floating point type, whatever that is. For example:

julia> promote(Float16(1.0f0), typemax(Int))
(Float16(1.0), Inf16)

julia> promote(Float32(1), typemax(Int32))[2] |> Int 
2147483648

julia> typemax(Int32)
2147483647

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Correct @vtjnash. I can make the change to "Mixtures of integers and floating-point values are promoted to the floating-point type." if this is the wanted behavior and the current implementation is not the problem?

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My point is that some people might find this quite unexpected:

julia> max(Float16(1), typemax(Int64))
Inf16

julia> versioninfo()
Julia Version 1.8.5
Commit 17cfb8e65ea (2023-01-08 06:45 UTC)
Platform Info:
  OS: macOS (arm64-apple-darwin21.5.0)
  CPU: 10 × Apple M1 Max
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-13.0.1 (ORCJIT, apple-m1)
  Threads: 8 on 8 virtual cores
Environment:
  JULIA_NUM_THREADS = 8

with rationals are promoted to rationals. Rationals mixed with floats are promoted to floats.
Complex values mixed with real values are promoted to the appropriate kind of complex value.

That is really all there is to using promotions. The rest is just a matter of clever application,
the most typical "clever" application being the definition of catch-all methods for numeric operations
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