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Suppose we have a class named Calculator. There's a class method in it, called runProgram. If I wanted to call this class method, inside the class's implementation, what would the difference between these two be:

[Calculator runProgram]

OR

[self runProgram]

Are these both the same?

Alexander Abakumov
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Milad
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1 Answers1

34

If inside an instance method:

[self runProgram]

in this, self means the object instance itself, and thus it will generate a runtime error. You want to use

[[self class] runProgram]

instead.

However, if you call this method from another class method, then

[self runProgram]

is correct, since now self refers to the class itself. I'd discourage to use

[Calculator runProgram]

because then subclasses of the class would erroneously call the superclass' (Calculator's) method instead of a possibly overridden method.

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    With the caveat that `[Calculator runProgram]` is correct for classes that are explicitly nothing to do with `Calculator`, ala usage of the various factory methods? – Tommy Apr 29 '12 at 05:41
  • +1: Of course, since there is no other method for them! But OP asked about calling the method in the implementor class itself. –  Apr 29 '12 at 05:47