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Self. _x is the automatically created instance variable.
For example, you define the following attribute:

@property(nonation, strong) NSString *x;

There is a bunch of hidden (simplified) code as follows:

NSString *_x;

-(NSString *)x {
    return _x;
}

-(void)setX:(NSString *)x {
    _x = x;
}

I guess your lazy loading code overloads the get method of the attribute. Self.x actually calls the [self x] method. If you use self.x in the get method, then self.x calls it again. , [self x] method, this is infinite recursion.

If it is referenced, there will be no difference. It is the same pointer. If it is assigned, there is a difference. self.xx=oo First, xxretaincount -1 and then retain oo _XX is copied to point directly to oo. There is no retain step. Nor

I just guessed that you might be:

self.some = [self some];
-(type)some{
    self.some = [...];
}

Then when you call self.some, it is equivalent to using [self some], and self.some in some calls [self some] again. . . A loop is formed. . .

Underscore means direct access, bypassing set and get. .