[bug #47618] NSPredicate: SELF implemented incorrectly

[Niels Grewe]

URL:
  <http://savannah.gnu.org/bugs/?47618>

                 Summary: NSPredicate: SELF implemented incorrectly
                 Project: GNUstep
            Submitted by: thebeing
            Submitted on: Mo 04 Apr 2016 14:56:49 GMT
                Category: Base/Foundation
                Severity: 3 - Normal
              Item Group: Bug
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

The SELF expression in NSPredicate is implemented in a way that only allows it
to be used as LHS or RHS expression in an NSComparison predicate. 

In particular, the following is legal under Cocoa:

  NSDictionary *a = [NSDictionary dictionaryWithObjectsAndKeys: 
    @"2", @"foo", nil];
  NSPredicate *p = [NSPredicate predicateWithFormat: @"SELF.foo <= 2"];
  [p evaluateWithObject: a];

The base implementation gives you:

Uncaught exception NSInvalidArgumentException, reason:
[GSEvaluatedObjectExpression-keyPath] should be overridden by subclass

You can even do more complicated expressions such as "bar[SELF.foo]", where
SELF is not a top-level expression in Cocoa.

The reason is that GSEvaluatedObjectExpression is created as a singleton, and
always returns itself from expressionValueWithObject:context:, and there is
some pointer equality checking in NSComparisonPredicate  to make it work for
the really simple case (self == 'foo'). That totally sounds like premature
optimisation to me, btw.





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