[swift-evolution] idea: immutable setters for structs and tuples?

[James Campbell]

Yeah a way to have a function that mutates a struct return a new copy with
that mutation would be awesome ! Rather than mutating in place.

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On Wed, Mar 23, 2016 at 2:28 PM, William Dillon via swift-evolution <
swift-evolution at swift.org> wrote:

> I like this.  I’m always annoyed when I need var just because I can’t get
> all my initialization done with let.
>
> - Will
>
> > On Mar 23, 2016, at 2:32 AM, Brent Royal-Gordon via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> >> let john = {firstName="John"; lastName="Doe"}
> >> let alice = {john with FirstName="Alice"}
> >>
> >>  Current way to do this in Swift is:
> >>
> >> let john = (firstName:"John", lastName:"Doe")
> >> var alice = john
> >> alice.firstName = "Alice"
> >
> > I think this is better modeled in Swift as something like:
> >
> >       let john = (firstName:"John", lastName:"Doe")
> >       let alice = with(john) {
> >               $0.firstName = "Alice"
> >       }
> >
> > `with` would be something like:
> >
> >       func with<Value>(value: Value, function: Value throws -> Void)
> rethrows -> Value {
> >               var mutableValue = value
> >               return try function(&mutableValue)
> >       }
> >
> > This would serve many different purposes:
> >
> > * If the value is a value type, allows you to return a modified copy
> > * Allows you to customize a value's properties immediately after
> initializing it, which many people have asked for
> > * Acts as a `tap` function when the block doesn't change the value (see <
> http://ruby-doc.org/core-2.3.0/Object.html#method-i-tap>)
> >
> > --
> > Brent Royal-Gordon
> > Architechies
> >
> > _______________________________________________
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> > swift-evolution at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-evolution
>
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