Detailed explanation of named return values ​​of Golang functions

Golang is a programming language that develops in the field of concurrency. In order to allow developers to process data and status more conveniently, it has designed some very convenient and practical features and syntax, including named return values ​​of functions. In this article, we’ll dive into the usage and caveats of this feature.

1. The concept of named return values

In functions, we often need to return some values. However, explicitly declaring the values ​​to be returned in the function parameter list sometimes seems verbose and confusing. Not easy to understand. Therefore, Golang introduced the concept of named returns (Named Returns) to solve this problem.

Using named return values, we can use the returned value as part of the function name when declaring the function, so that we can use these variable names directly in the function body without using the return keyword. In this way, when the function execution ends, the declared return value variable will automatically return. This feature is widely used to handle multiple return values ​​from functions.

2. Usage method

Let’s look at some examples of using named return values.

1. Basic usage

   func split(sum int) (x, y int) {
    x = sum * 4 / 9
    y = sum - x
    return
   }
   
   func main() {
    fmt.Println(split(17))
   }

   In the split function, we use named return values ​​x and y, and there is no return keyword inside the function body. In the split function, we can implicitly return x and y simply by providing an empty parameter list in the return statement.

2. The parameters have the same name as the named return value

   func add(x, y int) (sum int) {
    sum = x + y
    return sum
   }

   In the add function, sum is the named return value, and x and y are parameters. At the same time, sum can also be used internally as a parameter. In this case, sum uses variables inside the function rather than parameters.

3. Name only part of the return value

   func rectProps(length, width float64) (area, perimeter float64) {
    if length <= 0 || width <= 0 {
        return 0, 0
    }
   
    // 四边形周长和面积的计算
    perimeter = 2 * (length + width)
    area = length * width
    return area, perimeter
   }

   In the rectProps function, we only named area and perimeter as return values, but did not name the input parameters of the function. In this case, we need to use the return statement to explicitly specify the return value, and cannot use an empty parameter list.

3. Notes

1. Named return values ​​are not pointer types
   Named return values ​​are not pointer types, so they do not need to be declared before use or allocate memory. When functions are called, they are automatically declared. But using unallocated memory variables in a function will cause panic. Therefore, when declaring a named return value, make sure the variable is in the correct state before use.
2. Only applies to single return values
   Named return values ​​are only used for a single return value in a function, not for multiple return values. If a function needs to return multiple variables, they still need to be explicitly declared in the function signature.
3. Don’t abuse return value variables
   When using named return values, return value variables should be used with caution. If a function has multiple return values, but only some variables are named, then the unnamed variables cannot be manipulated directly, and they need to be ignored using the whitespace identifier "_".
4. Pay attention to the type matching of the return value
   When using named return values, you should pay attention to the type matching of the return value. If the type of the return value is inconsistent with the type declared in the function signature, the compiler will report an error.

4. Summary

In Golang functions, named return values ​​are a very practical feature, which can make it more convenient and simplify the code when we deal with multiple return values. Through the introduction of this article, I believe readers will have a deeper understanding of the usage and precautions of named return values ​​in Golang programs.

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