[swift-evolution] [Proposal] function "return" optional keyword.

[Craig Cruden]

The difference between issuing return embedded in multiple locations to reduce verbosity is actually slightly more than extra verbosity it is actually a different execution path.

In my last example (Scalaish).  The last and only expression in the function is the whole match case - it terminates at the end of the function.

  def f2(input: Integer) : Integer = {
    input match {
        case _ if input > 10 => 10
        case _ if input < 0  => 0
        case _ => input
    }
  }

Whereas if you sprinkle in returns as such, you are actually changing the execution path:

  def f2(input: Integer) : Integer = {
    input match {
        case _ if input > 10 => return 10  <— function terminates here
        case _ if input < 0  => return 0  <— function terminates and here
        case _ => return input  <— <— function terminates and here
    }
  }

A move towards spaghetti like code.

Now if you were to add an extra expression like using an intermediate value.

  def f2(input: Integer) : Integer = {
    let x = input match {
        case _ if input > 10 => 10  // no longer terminates here
        case _ if input < 0  => 0  // no longer terminates here
        case _ => input   // no longer terminates here
    }
    x /2  // or return x/2
  }

You would have had to go back and modify the original execution path with all the embedded returns which can also be a source of unwanted defects if one is missed (in larger functions).


> On 2015-12-21, at 3:29:27, Radosław Pietruszewski <radexpl at gmail.com> wrote:
> 
> I honestly don’t have a problem with having to say `return` inside functions. That’s not necessarily a -1, but I’m reluctant to say +1 when _even I_ don’t really have the problem with extra verbosity.
> 
> *However*, as others pointed out, having to type `return` is a bit tiring in the context of a computer property’s “get”:
> 
>> var twiceSomething: Int { self.something * 2 }
> 
> — Radek
> 
>> On 19 Dec 2015, at 14:30, Craig Cruden via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>> When writing short functional code in a function it would be nice if the return keyword were an optional keyword. 
>> 
>> Just return the last evaluated expression.
>> 
>> 
>> i.e.
>> 
>>     func flipFunc<T, U>(arg1: T, arg2: U) -> (U, T) {
>>         (arg2, arg1)
>>     }
>> 
>> 
>> The keyword return would still be there for breaking out of a function.
>> 
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> 

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