[swift-evolution] [proposal] Allow "let" for computed properties which only reference immutable data

[Sean Heber]

I kind of agree with the logic of that, but imagine the following:

class Test {
  let hello = “hello”
  var subject = “world”
  var phrase: String { return hello + “, “ + subject }
}

In this scenario, “subject” can be changed.. and that changes the result of “phrase”. Things like this are why computed properties are “var”.

l8r
Sean


> On May 11, 2016, at 8:25 AM, Alexander Momchilov via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I came an interesting SO question which pointed out a strange quirk: a computed property must always use the "var" keyword, even if it's read-only, and only referencing other immutable data.
> 
> class Test {
> 
>   
> let hello = "hello"
> 
>   
> let world = "world"
> 
>   
> var phrase: String { //why must this be 'var'?
> 
>      
> return self.hello + self.
> world
>   
> }
> }
> It would be more appropriate for such a read-only, immutable property, to use the "let" syntax, so that its immutability is correctly expressed.
> 
> Thoughts?
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