What does golang assertion mean?

In the Go language, assertion is a type conversion operation used to convert the value of an interface type to a specific type. Interface types can represent any type of value in the Go language, but in some cases, the value of the interface type needs to be converted into a specific type for operation. Assertions in the Go language are usually implemented using type assertion expressions, whose syntax is "value, ok := interfaceValue.(Type)".

The operating system for this tutorial: Windows 10 system, go1.20.1 version, Dell G3 computer.

In the Go language, assertion is a type conversion operation used to convert the value of an interface type into a specific type. Interface types can represent any type of value in the Go language, but in some cases, we need to convert the value of the interface type into a specific type for operation.

Assertions in Go language are usually implemented using type assertion expressions, whose syntax is:

value, ok := interfaceValue.(Type)

Among them, interfaceValue is an interface A value of type, where Type is the concrete type to be asserted. The assertion expression returns two values. The first value is the converted value of the specific type, and the second value is a Boolean value indicating whether the assertion was successful. The second value is true if the assertion succeeds, false otherwise.

Here is a simple example:

var i interface{} = "hello"
s, ok := i.(string)
if ok {
    fmt.Println(s) // 输出为 "hello"
} else {
    fmt.Println("断言失败")
}

In the above example, We assert an interface type value i as type string and assign the result to s and ok. If the assertion succeeds and the value of ok is true, we can use s to operate on string type values. If the assertion fails, ok evaluates to false and we can perform error handling as needed.

It should be noted that if the value of the interface type is not the type to be asserted, the assertion operation will trigger a runtime panic. Therefore, when performing assertion operations, it is recommended to use the above form with a second return value to facilitate safe type conversion.

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