[swift-evolution] [Discussion] "with" statement/method

[Vladimir.S]

On 22.04.2016 14:02, Joanna Carter wrote:
 > As much as I detested the 'with' construct in Delphi, with all its 
accompanying opportunities for errors of scope, if you really think it a 
good idea, then you need to consider the possibility of those who want to 
'with' more than one target. In which case, the use of $0, $1, etc would 
seem logical, although not necessarily very readable.
 >
 > Joanna
 >
 > --
 > Joanna Carter
 > Carter Consulting
 >
 > (de mon iPhone)
 >

Actually we can "manually" now implement the very clean and handy "with" 
(including with more than 1 "target") like this:

(I propose to include such kind of "with" feature to language or to 
standard classes/protocols to be able to use it out-of-box for any 
class/structure, not for some we have to apply manually)

class A {
     var x = 0
     var y = 0
     var z = 0

     func with(block: (this: A)->()) -> Self {
         block(this: self)

         return self
     }

     func with<T>(another: T, block: (this: A, that: T)->()) -> Self {
         block(this: self, that: another)

         return self
     }
}

var myFirstVeryLongInstanceName = A().with {
     $0.x = 1
     $0.y = 2
     $0.z = 3
}

var mySecondVeryLongInstanceName = A().with {new in
     new.x = 11
     new.y = 12
     new.z = 13
}

myFirstVeryLongInstanceName.with {my in
     my.x *= 1
     my.y *= 2
     my.z *= 3
}

mySecondVeryLongInstanceName.with(myFirstVeryLongInstanceName) {to, from in
     to.x = from.x * 10
     to.y = from.y * 20
     to.z = from.z * 30

     print(from.x)
     print(to.x)
}

mySecondVeryLongInstanceName.with(myFirstVeryLongInstanceName) {
     $0.x = $1.x * 100
     $0.y = $1.y * 200
     $0.z = $1.z * 300

     print($1.x)
     print($0.x)
}