Test.j

CPLogRegister(CPLogPrint);

@import <Foundation/Foundation.j>

@implementation Test : CPObject
{
    CPNumber ivar1;
    CPNumber ivar2;
}

- (void)trick:(JSObject)eval_func
{
    ivar1 = ivar2 = 5;
    eval("ivar1 = 6");
    eval_func("ivar2 = 6");
    CPLog(ivar1); // 6
    CPLog(ivar2); // 5 ?!
}

@end

[[[Test alloc] init] trick:eval];
CPLog(ivar2); // 6 ... *shakes head*
CPLog(ivar1); // Error, as it should be.