New JEP: Switch Expressions for the Java Language

[forax at univ-mlv.fr]

----- Mail original -----
> De: "Brian Goetz" <brian.goetz at oracle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>, "amber-spec-experts" <amber-spec-experts at openjdk.java.net>
> Cc: "Stephen Colebourne" <scolebourne at joda.org>
> Envoyé: Mardi 12 Décembre 2017 15:25:07
> Objet: Re: New JEP: Switch Expressions for the Java Language

>> to summarize,
>> we enhance le old switch by adding comma separated list of case values and by
>> adding null as a possible pattern, and a warning if there is no default or the
>> default is not at the ends,
>> then we add an expression switch which extends the old switch as a poly
>> expression with no fall through (make no sense), no weird scoping rules, the
>> compiler emits an error if the switch is not exhaustive (need a default at the
>> end apart for enums).
> 
> Right.
> 
>> what i'm currently doing with switch is using statement switch + return as a
>> poor's man expression switch
> 
> Very common!
>> I tend to refactor by introducing a method
> Essentially, trying to make DA work for you.
>> But if we support expression block in the expression switch, the two forms are
>> very close syntactically,
>> by example, can you find the difference between
>>    return switch(name) {
>>        case "red" -> {
>>          return Color.RED;
>>        };
>>        case "blue" -> {
>>          return Color.BLUE;
>>        };
>>        default -> {
>>          throw new AssertionError("invalid " + name);
>>        };
>>    };
>> and
>>    switch(name) {
>>        case "red": {
>>          return Color.RED;
>>        };
>>        case "blue": {
>>          return Color.BLUE;
>>        };
>>        default: {
>>          throw new AssertionError("invalid " + name);
>>        };
>>    };
>> this is far from obvious, and as a dev you have to because the semantics are
>> differents.
> 
> The main difference is the unfortunate pun between local and nonlocal
> return.
> 
>> I wonder if we should either make the syntactic difference more clear
> 
> Open to suggestions.

Use 'when' or 'match', with no 'case' and '_' instead of 'default' like in Kotlin/Scala (Koala) ?

  return match(name) {
    "red" -> Color.RED;
    "blue" -> {
      return Color.BLUE;
    }
    _ -> throw new AssertionError("invalid " + name);
  };

with the curly braces after match, it's not a valid method call so 'match' can be local keyword.

cheers,
Rémi