在（）中包装类型有什么作用，什么时候应该使用它？ Golang [重复]

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• Is this casting in golang? 1 answer

What exactly does wrapping a type in () do exactly and when should I use it? E.g. blah.(*int)

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Answer 1

It's a type assertion. Type assertions are used to extract the value in an interface type as some other type.

The expression blah.(*int) asserts that the type of the value in blah is *int. If the assertion holds, then the value of the expression is the value stored in blah as a *int. If the assertion does not hold, then the expression panics.

A special form of a type assertion can be used in an assignment to test the assertion:

 ip, ok := blah.(*int)

If the value in blah is of *int, then the value is stored in ip and ok is set to true. Otherwise, ip is set to the zero value and ok is false.