RFC: Throw an error when coalesce is passed only nothing/missing arguments #27157
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ararslan
reviewed
May 18, 2018
base/some.jl
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| for T in (:Nothing, :Missing) | ||
| @eval begin | ||
| coalesce(x::$T, y::Union{Nothing, Missing}) = | ||
| throw(ArgumentError("coalesce requires that least one argument differs from `nothing` or `missing`; " * |
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The line here is pretty long. I'd suggest changing the semicolon to a period and the space after it to a newline. Not a big deal though.
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Fast! I wasn't sure what's the convention about this. It's indeed problematic in the doctest.
Remove the one-argument method, which does not allow passing a replacement value which can never be nothing/missing. The old behavior can still be obtained by passing Some(nothing)/Some(missing) as last argument. Also add a tests for recursively wrapped values like Some(Some(1)), and remove useless 'using Base: coalesce' statements (from the time when it was not exported).
Used in one place in Base, and it's the only way of unwrapping Some.
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If this PR is merged I would recommend to update documentation of |
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I think this is going in the right direction, but it seems really weird to me that |
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Remove the one-argument method, which does not allow passing a replacement value which can never be nothing/missing. The old behavior can still be obtained by passing
Some(nothing)/Some(missing)as last argument.Possible fix for #26927.
The advantage of this PR is that it implements a strict subset of the previous behavior. So if we change our minds and decide to allow returning
nothing/missingwhen all arguments arenothing/missing(as in SQL and dplyr), it won't break anything.EDIT: instead of throwing an error, we could first print a deprecation.
EDIT2: the last commit also implements the proposal made by @Keno at #26927, i.e. when
nothingandmissingare mixed only the first one is replaced, and the other is considered as non missing and therefore returned as-is.