CODEWITHSUNDEEP
iosobjective-ccompare
Fogmeister
Fogmeister

Reputation: 77631

iOS compare function

I'm trying to understand what the standard way of writing a compare function is.

If I have an object Person with a property age and want to write my own compare function. I want to use it so that the Person objects are ordered from low age to high age.

i.e.

Person *young = [[Person alloc] initWithAge:10];
Person *old = [[Person alloc] initWithAge:80];

If I now run [young compare:old] should this return NSOrderedDescending or NSOrderedAscending?

I'm not sure which object is ascending or descending from which object (if that makes sense).

Upvotes: 0

Views: 659

Answers (2)

Tommy
Tommy

Reputation: 100622

The result of:

[obj1 compare:obj2]

Should be:

  • NSOrderedAscending if when written as 'obj1, obj2' the objects are in ascending order;
  • NSOrderedDescending if when written as 'obj1, obj2' the objects are in descending order;
  • NSOrderedSame otherwise.

So you should see:

[@2 compare:@3] == NSOrderedAscending
[@"b" compare:@"a"] == NSOrderedDescending

etc. The way to remember it is to think about reading from left to right in whoever is doing the calling.

Upvotes: 2

Paul.s
Paul.s

Reputation: 38728

The easiest way is to just lean on existing implementations

- (NSComparisonResult)compare:(Person *)other;
{
  return [@(self.age) compare:@(other.age)];
}

Upvotes: 2

Related Questions