LLVM Enhancement: @switch

Number:rdar://14557382 Date Originated:Jul 26 2013
Status:Open Resolved:
Product:LLVM Product Version:
Classification:Enhancement Reproducible:N/A

The classic C statement is useless for use in Objective-C if you want to use NSString literals as constants for the cases. This enhancement request is for adding an object-oriented version of the switch to Objective-C.

For example this could look like this:

   define MyBarConstantValue @"bar"

    NSString *string = @"foo";
   @switch (string) {
         // statements

         // statements


While a classic switch would do an == comparison between the expression and the labels this enhanced version would instead use isEqual: for the comparison. Otherwise the syntax would be identical.

Using this enhancement you could use any NSObject subclass which implements isEqual:. This would eliminate the need for creating enums for situations where an option is indeed an NSString. The above example currently has to be written:

   if ([string isEqual:@"foo"]) {
      // statements
   } else if ([string isEqual:MyBarConstantValue]) {
      // statements
   } else {
      // statements

This is harder to parse than using the proposed @switch statement. Also this doesn't allow for a "fall-through" for a few options by omitting the break statement. So this would also have to be smart to resolve this scenario.


Remember that NSString has its own special method, -isEqualToString:

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