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[SE-0439] Editorial clarifications on trailing comma support #3057

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[SE-0439] Editorial clarifications on trailing comma support #3057

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b6f3cb8
[SE-0439] Editorial clarifications on trailing comma support
xwu Dec 17, 2025
fdf2433
[SE-0439] Fixup to use a more standard spelling for initialization
xwu Dec 17, 2025
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10 changes: 9 additions & 1 deletion proposals/0439-trailing-comma-lists.md
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Expand Up @@ -146,14 +146,20 @@ This proposal adds support for trailing commas in symmetrically delimited comma-
}
```

- Generic parameters.
- Generic parameter lists and generic argument lists.

```swift
struct S<
T1,
T2,
T3,
> { }

let s = S<
T1,
T2,
T3,
>()
```

- String interpolation.
Expand All @@ -166,6 +172,8 @@ This proposal adds support for trailing commas in symmetrically delimited comma-

Trailing commas will be supported in comma-separated lists when symmetric delimiters (including `(...)`, `[...]`, and `<...>`) enable unambiguous parsing.

Note that the requirement for a comma-separated list means that `let x: [Int,] ❌` will not be supported, since a list of types is never supported in that context. Likewise, built-in attributes that don't parse their arguments as a comma-separated list will not support trailing comma, such as `@inline(never,) ❌`.

Note that the requirement for symmetric delimiters means that the following cases will not support trailing comma:

- `if`, `guard` and `while` condition lists.
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