[swift-evolution] [Proposal] Set literal and Set type syntax

[ilya]

Indeed, Set<T> is basically Dictionary<T, Void>
If we really need a separate syntax for sets then perhaps

var set1: [Int:]
var set2 = [2, 3, 5:]
set1= set2

will be most logical.

On Tue, Jan 19, 2016 at 20:12 Will Entriken via swift-evolution <
swift-evolution at swift.org> wrote:

> Another interpretation is that a Set *is* indexed, and its value is
> nonexistent. Or, in other words:
>
> var x = [String: ()]
> var y = [String: ()]()
>
> Literals might be
>
> var z = ["bourbon": (), "scotch": (), "beer": ()]
>
> or more succinctly
>
> var a = ["bourbon": (), "scotch", "beer"]
>
> Other choices like Void or nil may be more appropriate.
>
>
> On Mon, Jan 18, 2016 at 4:24 PM, Michael Henson via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Swift currently has literal and type shorthand syntax for native Array
>> and Dictionary types, but not the Set type. It would be useful to have a
>> literal shorthand for Set as well.
>>
>> The existing productions for array and dictionary literals and types
>> share brackets as delimiters, differing only in the contents between the
>> brackets. That poses a slight problem for Set because any syntax, to be
>> useful, must also be easily distinguishable from the other types.
>>
>> Consider that Arrays and Dictionaries are both naturally indexed
>> collections. Arrays by the integer value of the order of items in the
>> collection, usually implicitly, and Dictionaries by the hashed key
>> associated with each value.
>>
>> Arrays, implicit index:
>>
>> let array = ["a", "b", "c"]
>> var array: [String]
>> var empty: [String] = []
>>
>> Dictionaries, explicit index:
>>
>> let dictionary = ["a": 1, "b": 5, "c": 9]
>> var dictionary: [String: Int]
>> var empty: [String: Int] = [:]
>>
>> Sets, by contrast, have no particular order and no "key". Even though the
>> Set is enumerable and iterable, it isn't indexed. With that in mind, we can
>> declare that a Set literal or Set type literal should distinguish itself by
>> declaring that it has no index.
>>
>> The Set literal could be:
>>
>> let set = [ _: "a", "b", "c" ]
>> var set = [ _: String ]
>> var empty: [ _: String ] = [_:]
>>
>> In the grammar:
>>
>> set-literal -> [ _ : array-literal-items[opt] ]
>> literal-expression -> array-literal | dictionary-literal | set-literal
>>
>> set-type -> [ _ : type ]
>> type -> array-type | dictionary-type | set-type | ... etc.
>>
>>
>> Examples:
>>
>> let x = [ _: "A", "B", "C" ]
>> let y: [ _: String ] = [ _: ]
>>
>>
>> Alternatives considered:
>>
>> Without literals, declaring a Set type is straightforward, easy to
>> recognize, and not much more verbose. There might not be enough of a
>> difference to justify special syntax in the core language.
>>
>> Mike
>>
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>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
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