Stack objective-c

stack.h

//
//  Stack.h
//  testing
//
//  Created by Roman Barzyczak on 16.02.2014.
//
//

#import <Foundation/Foundation.h>

typedef struct StackElement StackElement;

struct StackElement {
	__unsafe_unretained id value;
	StackElement *prev;
};

@interface Stack : NSObject

- (void) push:(id)value;
- (id) pop;
- (BOOL) isEmpty;
@end

stack.m

//
//  Stack.m
//  testing
//
//  Created by Roman Barzyczak on 16.02.2014.
//
//

#import "Stack.h"



@interface Stack ()

@property (nonatomic) StackElement *top;

@end

@implementation Stack

- (BOOL) isEmpty {
    return self.top == nil ? YES : NO;
}

- (void) push:(id)value {
	StackElement *stackElement = malloc(sizeof(StackElement));
	stackElement->value = value;
	
    
	if([self isEmpty]) {
		stackElement->prev = NULL;
		self.top = stackElement;
    } else {
        StackElement *lastTop = self.top;
        self.top = stackElement;
        stackElement->prev = lastTop;
    }
}

- (id) pop {
    if([self isEmpty]) {
        return nil;
    }
	StackElement *lastTop = self.top;
	self.top = self.top->prev;
	return lastTop->value;
}

@end