golang assertion implementation

Golang is a language with powerful concurrency and system programming capabilities. It is a compiled language designed to make programming faster and easier. Assertions are an important concept in Golang. It allows programmers to "assert" the type of a variable or interface while writing code, so that the correct type can be checked at runtime.

1. What is an assertion?

Assertion is a type verification method that can determine whether a variable or interface belongs to a certain type when the code is running. Typically, assertions are used to check the correctness of code post-compilation and to detect and resolve errors early.

In Golang, assertions are implemented through the keyword "interface{}". interface{} represents an empty interface, which can accept all types of data. Empty interfaces can be converted to other concrete types by using type conversions.

For example, the following code uses the keyword "interface{}" to implement assertions:

var i interface{} = "Hello"
s := i.(string)
fmt.Println(s)

In this example, the empty interface "interface{}" is used to save the "Hello" string. Then, use assertion "i.(string)" to convert it to string type. Finally, use "fmt.Println(s)" to print the string "Hello".

2. Three assertion methods in Golang

In Golang, there are three ways to assert, namely type checking statements, type assertion statements and type judgment statements:

1. Type check statement

value, isType := someVariable.(Type)

Among them, "value" represents a variable that can store the converted value; "isType" is a Boolean type variable. If the conversion is successful, it will be Set to True.

For example:

var i interface{} = 55
s, ok := i.(string)
if ok {
  fmt.Printf("%q
", s)
} else {
  fmt.Printf("unexpected type %T
", i)
} 

In this example, the variable "i" is an empty interface and stores the Integer type value "55". Convert it to string type by using the assertion "s, ok := i.(string)" and store the converted value in the "s" variable; store the conversion result in the "ok" variable. Then, the conversion result is judged through the conditional statement "if ok". If it is a string type, the string "55" is printed, otherwise "unexpected type" is printed.

2. Type assertion statement

value := someVariable.(Type)

The type assertion statement is similar to the type checking statement, but it does not return a Boolean value whether the conversion is successful. If the type conversion fails, the program will crash and return a panic error.

For example:

var i interface{} = 55
s := i.(string) // panic: interface conversion: interface is int, not string

In this example, the variable "i" is an empty interface and stores the Integer type value "55". Although we intend to convert it to string type, the type assertion will throw a panic error, "interface conversion: interface is int, not string".

3. Type judgment statement

switch someVariable.(type) {
case Type1:
    // someVariable 为Type1类型
case Type2:
    // someVariable 为Type2类型
default:
    // someVariable 不是Type1或Type2类型
}

The type judgment statement is similar to the type check statement, but it does not return a Boolean value whether the conversion is successful. By using the type judgment statement, "switch someVariable.(type)" can determine the type of a variable and execute different code blocks according to its different types.

For example:

var i interface{} = 55
switch i.(type) {
case int:
  fmt.Println("i is an int")
case string:
  fmt.Println("i is a string")
default:
  fmt.Printf("Unexpected type %T", i)
}

In this example, the variable "i" is an empty interface and stores an Integer type value. By using the type judgment statement, "switch i.(type)" can determine the type of the "i" variable and execute the corresponding code block. Since "i" is an integer type, the code will print "i is an int".

3. Conclusion

In Golang, assertion is a commonly used technology. It allows programmers to check the type of variables or interfaces at runtime to prevent serious consequences caused by type errors later. In this article, we introduce three assertion methods in Golang, including type checking statements, type assertion statements and type judgment statements. Each assertion method has its unique advantages and limitations, and programmers can choose the method that suits them according to actual needs.

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