[swift-evolution] [Discussion] Here we go again: Extension Functions

[Eugene Gubin]

+1 very interesting idea

2016-02-26 9:09 GMT+03:00 Russ Bishop via swift-evolution <
swift-evolution at swift.org>:

> +1 to this or something like it.
>
> Right now I’m relying on crap^H^H^H^Hstuff like dispatch_get_specific to
> provide that kind of context without introducing something like Quick’s
> global “World”.
>
> Russ
>
> > On Feb 25, 2016, at 2:47 PM, Stephen Celis via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > I'm reopening a topic that has already been discussed here at length[1]:
> setup closures and `self`-binding closures.
> >
> > I've been wondering if Swift could adopt what Kotlin calls "extension
> function expressions"[2]. These would allow us to encode a closure's
> receiver type (`self`) into the closure type itself, providing a powerful,
> type-safe way to define DSLs.
> >
> > Erica's earlier draft proposed this builder pattern:
> >
> >    with let task = NSTask() {
> >        launchPath = "/usr/bin/mdfind"
> >        arguments = ["kMDItemDisplayName == *.playground"]
> >        standardOutput = pipe
> >    }
> >
> > With extension functions, we could approach something similar:
> >
> >    func with<T>(value: T, body: T.() -> ()) -> T {
> >        value.body()
> >        return value
> >    }
> >
> >    let task = with(NSTask()) {
> >        launchPath = "/usr/bin/mdfind"
> >        arguments = ["kMDItemDisplayName == *.playground"]
> >        standardOutput = pipe
> >    }
> >
> > Or, using the `then`[3] pattern:
> >
> >    protocol Builder {}
> >    extension Builder {
> >        func then(body: Self.() -> ()) -> Self {
> >            body()
> >            return self
> >        }
> >    }
> >    extension NSTask: Builder {}
> >
> >    let task = NSTask().then {
> >        launchPath = "/usr/bin/mdfind"
> >        arguments = ["kMDItemDisplayName == *.playground"]
> >        standardOutput = pipe
> >    }
> >
> > How about BDD-style frameworks (like Quick/Nimble[4] and Spectre[5])?
> >
> >    describe("a person") {
> >        let person = Person(name: "Kyle")
> >
> >        it("has a name") {
> >            try expect(person.name) == "Kyle"
> >        }
> >    }
> >
> > And HTML builders?
> >
> >    html {
> >        head { title("Hello, World!") }
> >    }
> >
> > And block-based, transactional APIs?
> >
> >    db.inTransaction {
> >        delete("users", "first_name = ?", ["Jake"])
> >    }
> >
> > The main benefits have been previously discussed:
> >
> > 1. The ability to remove noise ("$0" everywhere)
> > 2. The ability to avoid defining globals (in favor of a safer, scoped
> interface)
> >
> > Would such an enhancement be feasible?
> >
> > ---
> > Stephen
> >
> > Footnotes:
> >
> > [1] A probably-incomplete list:
> > - "Idea for enabling DSLs: bind to self in closures":
> https://lists.swift.org/pipermail/swift-evolution/2015-December/000114.html
> > - "Request for Discussion: Setup closures":
> https://lists.swift.org/pipermail/swift-evolution/2015-December/000211.html
> > - "Method cascading (was Re: Request for Discussion: Setup closures)":
> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151130/000729.html
> > - "Fluent syntax (replacing void with a useful default return value)":
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/374
> > - "Lexical scope statement (with .. do)":
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/1408
> > - "Scoped resources (like C# using statement)":
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/1641
> > - "Customized Inline Init Closure":
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/1946
> > - "Then Support":
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/2054
> > - "Draft proposal: multi-property assignment .= operator":
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/2960
> > - "Custom default names for arguments of closures":
> http://thread.gmane.org/gmane.comp.lang.swift.evolution/6969
> > - https://bugs.swift.org/browse/SR-160
> >
> > [2]
> https://kotlinlang.org/docs/reference/lambdas.html#function-literals-with-receiver
> > [3] https://github.com/devxoul/Then
> > [4] https://github.com/Quick/Quick
> > [5] https://github.com/kylef/Spectre
> >
> > _______________________________________________
> > swift-evolution mailing list
> > swift-evolution at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-evolution
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160226/dcca6a4a/attachment.html>