Andrey Breslav
36 lines
1.3 KiB
Plaintext
36 lines
1.3 KiB
Plaintext
h3. Equality
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In [Kotlin] there are two types of equality:
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* referential equality (two references point to the same object)
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* structural equality (a check for {{equals()}}
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h4. Referential equality
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In [Kotlin], there's no built-in operator to check for referential equality, for we believe that it is rarely needed. Instead, there's an [inline function|Functions#Inline functions] {{identityEquals()}} that can be called in the following way:
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{jet}
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a.identityEquals(b)
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// or
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a identityEquals b // infix call
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{jet}
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And returns *true* if and only if {{a}} and {{b}} point to the same object.
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h4. Structural equality
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Structural equality is checked by the {{==}} operation (and its negated counterpart {{!=}}). By [convention|Operator overloading#Equals], an expression like {{a == b}} is translated to
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{jet}
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a?.equals(b) ?: b.identityEquals(null)
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{jet}
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I.e. if {{a}} is not *null*, it calls the {{equals(Any?)}} function, otherwise (i.e. {{a}} is *null*) it checks that {{b}} is referentially equal to *null*.
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Note that there's no point in optimizing your code when comparing to *null* explicitly: {{a == null}} will be automatically translated to {{a.identityEquals(null)}}.
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h3. What's next
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* [Control structures]
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* [Function literals]
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* [Returns and jumps]
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* [Ranges]
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* [This expressions]
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* [Tuples]
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* [Type casts]
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