Proposal: adding value to 'break' statement

[ghost]

The idea is to modernize break statement in every construct where it's currently defined by adding a new parameter value. The general form of break statement becomes: break label->value; In this extended form, the keyword break can be omitted (it becomes redundant when -> is present), so we can write it as label->value, which further degenerates into ->value if the label is omitted.

Now every construct that currently supports break might be used as an expression:

final String numericString =
   switch (integer) {  
      case 1 : -> "uno";
      case 2 : print("debug print"); ->"dos";
      case 3 : -> "tres";
      default :-> "N/A";
   };
var x = for (int i=0; i<10; i++) {  
   if (someCondition(i)) -> i;
} 
if (x!=null) { // if the search is not successful, x is null
   // do something
}
// same for "while" block

It would probably make sense to also add support for "when" block (as a statement and as an expression):

var x = ...;
var y = when {
   case x <= 5: -> "a";
   case x > 5 && x < 10: -> "b"; 
   case x >= 10 && x < 20: -> "c"
   default: ->"d";
}

NOTE: the natural idea would be to extend the proposed syntax to block statement {...} thus turning it into block-expression, but it doesn't quite work out: block supports break only in a form break label. However, the following syntax is not valid in dart:
var x=label: {statements... break label; ...}

Anyway, block-expressions won't add too much power to the language: if anonymous methods (#260) are implemented, then we can always find a suitable receiver to achieve the same effect via anonymous method call obj.{...} that returns the result using a standard return statement.

[lrhn]

This would fit better into a setting where all statements have a value and can be used as expressions.
Then var x = label: { for (var something in somewhat) if (test) label -> value;}; could work.

We are a little hampered by labels not being in the same namespace as everything else. Otherwise we could just use break label value with both label and value being optional.

[nioncode]

@tatumizer why did you close this? Was this introduced into dart?