[swift-evolution] [Pitch] Allow numerical keywords in member references

Adrian Zubarev adrian.zubarev at devandartist.com
Thu Mar 9 01:46:22 CST 2017

I don’t have more precise examples except something like TCP socket error codes as an enum. The example with the number literal is actually really good, because it also shows the bad sides of the pitch. However we could allow numerical enum cases without any issues right?

Adrian Zubarev
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Am 9. März 2017 um 08:41:13, Slava Pestov (spestov at apple.com) schrieb:

On Mar 8, 2017, at 11:33 PM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:

I forget to mention, this should be also valid:

let `42` = 42


struct A {
    let `0` = 0

let number = A().0


This seems really confusing.

extension Int { var `0`: Int { return 0 } }

3.0 // is this a float literal?
3 .0 // member access?
.0 // this is actually a contextual member access, and not a literal ‘0.0’?

 I’d prefer if .0, .1, … were reserved for tuple fields; .0 is already not very descriptive, but at the very least if you see it in source code you know you have a tuple type and not something else.

Also the compiler’s name mangling relies on the fact that identifiers never begin with a numeric character or symbol.

Can you give a motivating example where allowing an identifier to start with a number actually helps readability?


Adrian Zubarev
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Am 9. März 2017 um 08:24:54, Adrian Zubarev (adrian.zubarev at devandartist.com) schrieb:

Hi Swift community, I’d like to pitch this idea again.

Swift already has the pitched feature, but it is exclusive for tuples only. SE–0071 allowed the use of keywords after the . in a member access, except for those keywords that have special meaning by using back-ticks. However, members starting with numbers are not special keywords and as already mentioned, numerical members are already allowed in tuples.

I propose to extend that capability to the whole language and make that behavior consistent. To disambiguate members starting with a number one would need to use back-ticks.

// Enum
enum ErrorCode : String {
    case `2345` = "my description for 2345"
    case `123a` = "my description for 123a"
    case `123b` = "my description for 123b"

let code = ErrorCode.2345

// Function
func `42foo`(label: Type, `12345`: Type, `0987something`: Type) { … }

// Tuple
(`1`: Int, `2`: Int)
My question is: would that be in scope for Swift 4?

Adrian Zubarev
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