NSNumber leaks using predicates

[javadude]

Hi guys,
I've got an object that takes an expression like "23.67*$MY_KEY" and a dictionary with the values mapping to the keys used in the expression. I pipe the key values into a NSPredicate and cast that to a NSExpression to evaluate the expression.

#import "ExpressionEval.h"

@implementation ExpressionEval

// Evaluates a math expression by substituting in values from a dictionary into known variables
+ (NSDecimalNumber *) calcExpresssion:(NSString *)expr  variables:(NSDictionary *)values error:(NSError **)err {
	NSDecimalNumber *result;
	NSNumber *tempNum;
	NSMutableDictionary *substituteValues = [NSMutableDictionary dictionary];

	// Cannot process if there is no expression
	if (!expr) {
		NSMutableDictionary *errorDetail = [NSMutableDictionary dictionary];
		[errorDetail setValue:@"Tried to calculate an expression that is nil" forKey:NSLocalizedDescriptionKey];
		*err = [NSError errorWithDomain:@"myDomain" code:100 userInfo:errorDetail];
		
		return nil;
	}
		
	NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
	[formatter setNumberStyle:NSNumberFormatterDecimalStyle];
	
	// Covert string values in dictionary with NSNumber instances
	for (NSString *key in values) {
		id value = [values objectForKey:key];
		
		if ([value isKindOfClass:[NSString class]]) {
			// If not a number nil will be returned, add to variable/value dictionary
			tempNum = [formatter numberFromString:value];
			if (tempNum != nil) {
				[substituteValues setValue:tempNum forKey:key];
			}
		}
	}
	
	[formatter release], formatter = nil;
	
	// Add a dummy right hand side to the equation if non exists
	NSMutableString *expression = [NSMutableString stringWithString:expr];
	NSRange range = [expr rangeOfString:@"=="];
	if (range.location == NSNotFound) {
		[expression appendFormat:@" == 0"];
	}
	
	@try {
		// Substite in variable values in expression
		NSPredicate *predicate = [NSPredicate predicateWithFormat:expression];
		predicate = [predicate predicateWithSubstitutionVariables:substituteValues];
		// Evaluate the left hand side of the expression
		NSExpression *algExpression = [(NSExpression *)predicate leftExpression];
		result = [algExpression expressionValueWithObject:nil context:nil];
	}
	@catch (id exception) {
		NSMutableDictionary *errorDetail = [NSMutableDictionary dictionary];
		[errorDetail setValue:@"Tried to calculate an expression that is nil" forKey:NSLocalizedDescriptionKey];
		*err = [NSError errorWithDomain:@"myDomain" code:100 userInfo:errorDetail];
		
		return nil;
	}
	
	return result;
}

@end

On running this with the Leaks performance tool Im getting the following leaks:

Leaked Object	#	Address	Size	Responsible Library	Responsible Frame
NSCFNumber	21	< multiple >	336	Foundation	getObjectValue
NSCFNumber	21	< multiple >	336	Foundation	getObjectValue

Im suspecting the NSMutableDictionary loaded with NSNumber instances. I have no idea what could be the problem here as I don't know the mechanics of the NSPredicate and NSExpression behind the scenes. Could anyone shine some light on a solution?

[javadude]

Aha, got it! It was coming from the NSNumberFormatter parsing non-numbers. I assumed it would be safe and merely return a nil but instead was causing leaks. Below is the fixed code snippet:

// Only convert to number is string is numeric
double holder;
NSScanner *scan = [NSScanner scannerWithString:value];
if ([scan scanDouble:&holder] && [scan isAtEnd]) {
	tempNum = [formatter numberFromString:value];
}
else {
	tempNum = nil;
}
			
// If not a number nil will be returned, add to variable/value dictionary
if (tempNum != nil) {
	[substituteValues setValue:tempNum forKey:key];
}