Why do we need to use @Synthesize?

We can use generated code like nonatomic, atmoic, retain without writing any lines of code. We also have getter and setter methods. To use this, you have 2 other ways: @synthesize or @dynamic: @synthesize, compiler will generate the getter and setter automatically for you, @dynamic: you have to write them yourself.@property is really good for memory management, for example: retain.How can you do retain without @property?

if (_variable != object)
{
    [_variable release];
    _variable = nil;
    _variable = [object retain];
}

How can you use it with @property?self.variable = object; When we are calling the above line, we actually call the setter like [self setVariable:object] and then the generated setter will do its job.