proposal: Go 2: Inline switch statement

[godalming123]

Author background

• Experience in go:
  I am a novice go programmer but know lots of other languages such as
• Experience in other languages
  • C - Maintain a 2K+ C code project

Related proposals

• Is this about generics?
  • If so, how does this relate to the accepted design and other generics proposals?
    • Their is one other proposal: proposal: Go 2: add a ternary conditional operator #33171 which is still being discussed
    • This also goes against the opinions of the go developers (https://go.dev/doc/faq#Does_Go_have_a_ternary_form), however much like in the proposal previously mentioned I think that this could make code cleaner and easier to read and have given 2 examples of this further down.

Proposal

• What is the proposed change?
  Add a way to return data in a switch statement to assign a variable or pass to a function argument
• Who does this proposal help, and why?
  It helps right slightly cleaner code for example (example syntax of this feature):

age := 42
ageDescription := switch age {
  case 0...5: "baby"
  case 6...18: "teenager"
  case 18...70: "adult"
  default: "elderly"
}

Is better then assigning an age var and ageDescription var, and then setting ageDescription in each case in the switch. This can become much worse if you are calling a function (example of what this would be like in old go):

someVar = 56
switch someVar {
  case 0..10:
    someFunc("very very long argument A", "very very long argument B", "very very long argument C", "very very long argument D", "your value that changes to A")
   case 10..25:
     someFunc("very very long argument A", "very very long argument B", "very very long argument C", "very very long argument D", "your value that changes to B")
 case 10..25:
     someFunc("very very long argument A", "very very long argument B", "very very long argument C", "very very long argument D", "your value that changes to C")
}
You can quickly see how this becomes hard to manage.

• Please describe as precisely as possible the change to the language.
  When the switch is used as a token and their is a token at the end of its value, then return that token and if their is no token then return an error when compiling.
• What would change in the language spec?
  Add a header on inline switches within the switch statements header that describes how they work, and in the code example add the switch statement example as seen above, or something similar.
• Please also describe the change informally, as in a class teaching Go.
  Switches can also return values like functions, to do this simple add a value at the end of each case statement to be returned.
• Is this change backward compatible?
  Yes.
• Orthogonality: how does this change interact or overlap with existing features?
  As I am still learning go I do not know many advanced futures, but from what I do know I don't think that it does interact with any.

Costs

• Would this change make Go easier or harder to learn, and why?
  If anything easier, because some code can become cleaner.
• What is the cost of this proposal? (Every language change has a cost).
  I can't think of any other then a little bit more complexity in the go compiler.
• How many tools (such as vet, gopls, gofmt, goimports, etc.) would be affected?
  gofmt may have to format this but I expect that it would be a simple change and no other tools are affected.
• What is the compile time cost?
  Any slowdown should not be perceivable compared to random error.
• What is the run time cost?
  I don't think that their is a runtime cost.

[seankhliao]

Duplicate of #44022