How to type check the return value of Golang function?

The function return value type checking mechanism in the Go language will perform type checking at compile time to ensure that the actual return value type of the function matches the return type declared by the function. Type checking rules include: the number of return type values ​​is consistent, and type compatibility judgment compatibility relationships include: the same basic type, pointer type and basic type, interface type and implemented interface type, slice type and array type that implements the interface{} interface.

Type checking of function return values ​​in Go

In the Go language, a function can return one or more values. To ensure that the returned value is of the correct type, type checking is required.

Type checking mechanism

The Go compiler will perform type checking at compile time. It checks whether the actual return value type of the function call matches the function's declared return type. If there is a mismatch, the compiler will report an error.

Type checking rules

Type checking follows the following rules:

• The number of values ​​in the actual return value list of the function must be the same as that of the function The number of return types in the declaration is the same.
• Each value in the actual return value list of a function must be type-compatible with the declared return type of the corresponding function.

Type Compatibility

In Go, type compatibility defines which types of values ​​can be assigned to each other. The following type relationships are compatible:

• The same basic type
• Pointer type and the basic type pointed to by the pointer
• Interface type and the type that implements the interface
• Slice type and array type that implements interface{}

Practical case

The following is a practical case Example showing how to type-check function return values:

package main

import "fmt"

func addNumbers(x, y int) (int, error) {
    if x < 0 || y < 0 {
        return 0, fmt.Errorf("invalid input: negative numbers not allowed")
    }
    return x + y, nil
}

func main() {
    result, err := addNumbers(3, 5)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("Result:", result)
}

In this example, the addNumbers function returns two values: an int value representing the result and an The error value indicates any error. The return type specified in the function declaration is (int, error), which means that the function must return an int value and an error value.

In the main function, the return value of the addNumbers function is assigned to the variables result and err. The compiler will check that the actual return value type matches the type returned in the function declaration. In this case, result is of type int and err is of type error, so the type check passes.

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