implement stack using linked list in swift

Swift program for implement stack using linked list. Here more information.

import Foundation
// Swift 4 program for
// Implementation stack using linked list

// Stack Node
class StackNode
{
	var data: Int;
	var next: StackNode? ;
	init(_ data: Int, _ top: StackNode? )
	{
		self.data = data;
		self.next = top;
	}
}
class MyStack
{
	var top: StackNode? ;
	var count: Int;
	init()
	{
		self.top = nil;
		self.count = 0;
	}
	// Returns the number of element in stack
	func size() -> Int
	{
		return self.count;
	}
	func isEmpty() -> Bool
	{
		if (self.size() > 0)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	// Add a new element in stack
	func push(_ data: Int)
	{
		// Make a new stack node
		// And set as top
		self.top = StackNode(data, self.top);
		// Increase node value
		self.count += 1;
	}
	// Add a top element in stack
	func pop() -> Int
	{
		var temp: Int = 0;
		if (self.isEmpty() == false)
		{
			// Get remove top value
			temp = self.top!.data;
			self.top = self.top!.next;
			// Reduce size
			self.count -= 1;
		}
		return temp;
	}
	// Used to get top element of stack
	func peek() -> Int
	{
		if (!self.isEmpty())
		{
			return self.top!.data;
		}
		else
		{
			return 0;
		}
	}
}
class Test
{
	static func main()
	{
		// Create new stack 
		let s: MyStack = MyStack();
		print("\n Is empty : "
			+ String(s.isEmpty()));
		// Add element
		s.push(15);
		s.push(14);
		s.push(31);
		s.push(21);
		s.push(10);
		print("\n Top  : "
			+ String(s.peek()));
		print(" Size : "
			+ String(s.size()));
		print("\n Is empty : "
			+ String(s.isEmpty()));
		// Delete Stack Element
		var data: Int = s.pop();
		print("\n Pop element "
			+ String(data));
		print(" Size : "
			+ String(s.size()));
		data = s.pop();
		print("\n Pop element "
			+ String(data));
		print(" Size : "
			+ String(s.size()));
	}
}
Test.main();

Output

 Is empty : true

 Top  : 10
 Size : 5

 Is empty : false

 Pop element 10
 Size : 4

 Pop element 21
 Size : 3