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https://github.com/JuliaLang/julia
19 April 2024, 06:28:37 UTC
Revision b3f766c2005acb9b3859b04f357de90355f38325 authored by Keno Fischer on 18 July 2023, 21:40:21 UTC, committed by GitHub on 18 July 2023, 21:40:21 UTC 
lowering: Disallow splatting in non-final default value (#50563)
 
Pop quiz: Do you know what the following will do?
```
julia> function g1(a=(1,2)..., b...=3)
    b
end

julia> g1()

julia> function g2(a=(1,2)..., b=3, c=4)
    (b, c)
end

julia> g2()

julia> function g3(a=(1,2)..., b=3, c...=4)
    (b, c)
end

julia> g3()

julia> g3(1)
```

I don't either and I don't think it's particularly well defined.
Splatting a default argument makes sense on the last argument, which can
be a vararg, and it is desirable to be able to specify the default for
the whole varargs tuple at once (although arguably that should just be
the non-`...` behavior, but that'd be too breaking a change). Ref
#50518. However, for other arguments, there isn't really a sensible
semantic meaning. This PR disallows this in lowering. This is
technically a minor change, but I doubt anybody is using this. Splatting
in default values wasn't really ever supposed to work anyway, it just
happened to fall out of our lowering.

---------

Co-authored-by: Jeff Bezanson <jeff.bezanson@gmail.com>
1 parent d270a71
History
Tip revision: b3f766c2005acb9b3859b04f357de90355f38325 authored by Keno Fischer on 18 July 2023, 21:40:21 UTC
lowering: Disallow splatting in non-final default value (#50563)
Tip revision: b3f766c
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CITATION.bib -rw-r--r-- 513 bytes
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CONTRIBUTING.md -rw-r--r-- 23.4 KB
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LICENSE.md -rw-r--r-- 1.3 KB
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julia.spdx.json -rw-r--r-- 35.8 KB
pkgimage.mk -rw-r--r-- 6.0 KB
sysimage.mk -rw-r--r-- 4.3 KB

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