What are type assertions in Go language?

Go language is a statically typed programming language. Type assertion (Type Assertion) is one of the ways to determine the specific value type stored in the interface variable in the program. In the Go language, an interface variable can store any type of value, but the type information stored in the interface variable is limited, and all types of operations cannot be performed on the interface variable. Therefore, in actual applications, we need to judge and convert the specific value types stored in interface variables. This is what type assertions do.

Type assertions in the Go language come in two forms: value type assertions and pointer type assertions. Value type assertions and pointer type assertions have slightly different ways of judging and converting the value types of interface variables.

Value type assertion:

The syntax format of value type assertion is as follows:

x.(T)

Among them, x is a variable of interface type, and T represents a specific type. This type assertion is true if x stores a value of type T, and false otherwise.

The result of the type assertion has two values. The first value is the value after x is converted to type T. The second value is a Boolean value indicating whether the result of this type assertion is true. The specific code implementation is as follows:

var x interface{}
x = "hello"

s, ok := x.(string)
if ok {
    fmt.Printf("x 类型为 string，值为 %s。
", s)
} else {
    fmt.Printf("x 不是 string 类型。
")
}

In the above code, an empty interface type variable x is first defined, and a string "hello" is assigned to the variable x. The value type assertion statement x.(string) attempts to convert the variable x to a string type, s represents the converted string, and ok represents whether the type assertion is successful. If ok is true, it means that the value type stored in x is a string type, and we can output the converted string s. If ok is false, it means that x is not a string type and the corresponding prompt information can be output.

Pointer type assertion:

The syntax format of pointer type assertion is similar to that of value type assertion, except that the pointer needs to be operated when asserting.

x.(*T)

Among them, *T represents the pointer type of type T. This type assertion is true if the value stored in x is of pointer type T, and false otherwise.

Like value type assertions, pointer type assertions also have two values. The first value is the value after x is converted into a T type pointer. The second value is a Boolean value, indicating the type assertion. Whether the result is true. The specific code implementation is as follows:

type Foo struct {
    bar string
}

func main() {
    var i interface{} = &Foo{"hello"}

    f, ok := i.(*Foo)
    if ok {
        fmt.Printf("i 是指针类型，指向 Foo 类型的变量，f.bar 的值为 %s。
", f.bar)
    } else {
        fmt.Printf("类型断言失败。
")
    }
}

In the above code, a structure of type Foo is defined, an empty interface variable i is defined in the main function, and a structure pointing to type Foo is defined The pointer is assigned to variable i. Pointer type assertion x.(*Foo) attempts to convert variable x into a pointer type pointing to a structure of type Foo, f represents the converted pointer, and ok represents whether the type assertion is successful. If ok is true, it means that the value type stored in x is a pointer type pointing to a Foo type structure, and we can output the field value in the structure pointed to by the pointer. If ok is false, it means that x is not a pointer type pointing to a Foo type structure, and the corresponding prompt information can be output.

Summary:

Type assertion is a commonly used way to operate interface variables in the Go language. Type assertions can determine the type stored in the interface variable, and then make corresponding adjustments to it. operate. There are two forms of type assertions in Go language, value type assertions and pointer type assertions. When using type assertions, you need to pay attention to error handling to avoid runtime errors.

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