[swift-evolution] [pitch] replace (if/guard) case = with ~=

[Nevin Brackett-Rozinsky]

While we’re on the subject, has there been any discussion about adding a
pattern matching operator with the polarity reversed?

To me at least it seems far more natural to write, eg., “case x =~
somePattern” and to read it as “x matches somePattern” rather than the
status quo “somePattern matches x”.

Nevin



On Mon, Oct 3, 2016 at 9:31 PM, Erica Sadun via swift-evolution <
swift-evolution at swift.org> wrote:

> *Resolved*: `if case 1...10 = myNumber { ... }` is an abomination.
>
> It confuses inexperience developers. At least those few who are
> aware of its existence. Using the assignment operator for pattern
> matching adds insult to injury.
>
> I far prefer
>     `if case .failure(let error) ~= result { ... } `
> to
>     `if case .failure(let error) = result {...}`
>
> Though worthy, this isn't a popular pattern.  A highly unscientific survey
> of
> gist reveal:
>
> * Gists using "if case": 94
> * Gists that could use "if let" instead of "if case": Approximately 94-ish
> * Gists using "guard case" (with significant overlap with "if case"): 54
> * Gists that could use "guard let" or "guard x != nil" or "guard x ==
> .enumeration" instead: About 54-ish
> * Standard library: 1 use of "guard case", 5 uses of "if case".
>
> *Note*:
>
> * I love `guard case`/`if case` for `Result` enumerations
> * I  love`for case let x? in [optionals]`.
>
> I don't expect changing `=` to `~=` would make a huge difference in
> adoption
> but it would satisfy  my inner code critic. Changing it would be breaking
> but as far as I can tell, it wouldn't really break *that* *much* *code*
>
> -- E
>
>
>
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