[swift-evolution] 100% bikeshed topic: DictionaryLiteral

Xiaodi Wu xiaodi.wu at gmail.com
Mon Jan 8 21:07:13 CST 2018

While there’s nothing specifically to do with a dictionary, it is a literal
in at least one essential respect. Like other literals, it doesn’t have a
type, but values that are expressed by them do acquire a type given the

Yes, it's not a dictionary, but neither is an integer literal an integer
(or even necessarily an integer you can create from such a literal: it can
be a floating-point value you create from that literal), etc. Would
"ordered collection of key-value pairs" be more "correct"? By the same
token, we ought to be renaming integer literals "ordered collection of
digits without interposed decimal point."

But essentially every user will have encountered this spelling in the
context of dictionaries: in other words, its name has a good basis in
reality because it is the (only) literal spelling that can be used to
create a dictionary, and when you say "hey, that spelling you use for a
literal to instantiate a dictionary in Swift," everyone will know what
you're talking about.

No, I think we ought to do nothing. It's not only "not bad," but as far as
I can tell quite superior to the alternatives in essentially every respect.
In the alternative, maybe "KeyValueLiteral" or something of that sort, but
I still would consider that to be strictly inferior to "DictionaryLiteral".

On Mon, Jan 8, 2018 at 20:24 Nate Cook via swift-evolution <
swift-evolution at swift.org> wrote:

> > On Jan 8, 2018, at 6:29 PM, Ben Cohen via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > There exists in the standard library a type `DictionaryLiteral` that
> deserves naming re-consideration before we declare ABI Stability, because
> it’s confusingly misnamed, being neither a Dictionary (it doesn’t provide
> key-based lookup of values) nor a Literal.
> >
> > Instead, it’s just an immutable collection of key-value pairs you can
> create _from_ a literal.
> >
> > I’m canvassing for opinions on what it ought to be called.  Some
> suggestions so far:
> >
> > - `AssociationCollection`: Following the term of art from some other
> languages. Slightly obscure-sounding to developers not already familiar.
> Also “association” and “associative” are confusingly similar, which brings
> back the is-this-a-dictionary problem.
> > - `KeyValueCollection`: Problematic because key-value comes up in a
> totally different context in Cocoa.
> > - `PairCollection`: “Pair” is kinda nondescript.
> > - Do nothing. It’s not so bad.
> Agreed so far, and I'd like to add CollectionOfPairs to the list.
> Some more fun facts about this type:
> - Besides Dictionary, it's the only other type in the standard library
> that is expressible by a dictionary literal
> - Unlike Dictionary, it *does* maintain the order of its pairs
> - Unlike Dictionary (part 2), it *doesn't* require the first element of
> the pairs to be Hashable
> Nate
> > The old name can live on indefinitely via a typealias (which has no ABI
> consequences, so could be retired at a later date once everyone has had
> plenty of time to address the deprecation warnings). Removing it as not
> carrying its weight (and instead using `[(Key,Value)]`, which is basically
> what it’s a wrapper for) is probably off the table for source stability
> reasons.
> >
> > Any further thoughts welcome.
> >
> >
> >
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