[swift-evolution] [Pitch] inout with capture variable

[Cao Jiannan]

I just want to demo how the inout capture works.
the demo code just want to capture value avoiding capture self.


> > On Oct 5, 2016, at 10:07 PM, Cao Jiannan<frogcjn at 163.com(mailto:frogcjn at 163.com)>wrote:
> > so if developer want to capture an variable inference, must declare a new variable.
> I don’t follow what you mean here.
> 
> > 
> > classA {
> > varvalue = 1
> > 
> > functest() ->() ->Int{
> > varcapturedValue =self.value
> > leteditInfo = { () ->Intin
> > capturedValue += 1
> > returncapturedValue
> > }
> > returneditInfo
> > }
> > }
> > 
> > leta =A()
> > 
> > leteditInfo =a.test()
> > print(editInfo()) // 2
> > print(a.value) // 1
> > 
> > print(editInfo()) // 3
> > 
> > print(a.value) // 1
> > 
> > what about:
> > 
> > classA {
> > varvalue = 1
> > 
> > functest() ->() ->Int{
> > leteditInfo = { [inout value] () ->Intin
> > capturedValue += 1
> > returncapturedValue
> > }
> > returneditInfo
> > }
> > }
> > 
> > leta =A()
> > 
> > leteditInfo =a.test()
> > print(editInfo()) // 2
> > print(a.value) // 2
> > 
> > 
> > print(editInfo()) // 3
> > 
> > print(a.value) // 3
> > 
> > 
> > 
> > 
> I’m not quite sure what you’re getting at, but this prints what you’re expecting in the output you have in the comments:
> 
> class A {
> var value = 1
> 
> func test() ->() ->Int {
> let editInfo = { () ->Int in
> self.value += 1
> return self.value
> }
> return editInfo
> }
> }
> 
> let a = A()
> 
> let editInfo = a.test()
> print(editInfo()) // 2
> print(a.value) // 2
> print(editInfo()) // 3
> print(a.value) // 3
> 
> 
> Mark
> 
> > 
> > >>On Oct 5, 2016, at 9:06 PM, Cao Jiannan via swift-evolution<swift-evolution at swift.org(mailto:swift-evolution at swift.org)>wrote:
> > >>
> > >>for example:
> > >>
> > >>var a = 1
> > >>
> > >>let block = { [inout a] in
> > >>a += 1
> > >>}
> > >>
> > >>block()
> > >>block()
> > >>
> > >>print(a) // 3
> > >This is already how captures work by default in closures and nested functions in Swift:
> > >
> > >var a = 1
> > >
> > >let block = { a += 1 }
> > >
> > >block()
> > >block()
> > >
> > >print(a) // prints 3
> > >
> > >
> > >If you want to capture something immutably you can put it in the capture list:
> > >
> > >var a = 1
> > >let block = { [a] in a += 1 } // error: left side of mutating operator isn't mutable: 'a' is a 'let' constant
> > >
> > >Mark
> > >
> > >>
> > >>
> > >>_______________________________________________
> > >>swift-evolution mailing list
> > >>swift-evolution at swift.org(mailto:swift-evolution at swift.org)
> > >>https://lists.swift.org/mailman/listinfo/swift-evolution
> > >
> > >
> > >
> 
> 
>