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Go - Functions

Every Go program has at least one function, which is main(). You can divide your code into separate functions.

A function declaration tells the compiler about a function name, return type, and parameters. A function definition provides the actual body of the function.

Functions are also known as method, sub-routine, or procedure.

Defining a Function

func function_name( [parameter list] ) [return_types]
{
   body of the function
}

A function definition in Go programming language consists of a function header and a function body.

  • Func − It starts the declaration of a function.

  • Function Name − It is the actual name of the function. The function name and the parameter list together constitute the function signature.

  • Parameters − A parameter is like a placeholder. When a function is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a function. Parameters are optional; that is, a function may contain no parameters.

  • Return Type − A function may return a list of values. The return_types is the list of data types of the values the function returns. Some functions perform the desired operations without returning a value. In this case, the return_type is the not required.

  • Function Body − It contains a collection of statements that define what the function does.

Example

The following source code shows a function called max(). This function takes two parameters product1 and product2 and returns the maximum between the two
/* function returning the max between two productbers */
func max(product1, product2 int) int {
    /* local variable declaration */
    result int

    if (product1 > product2) {
        result = product1
    } else {
        result = product2
    }
    return result
}

Calling a Function

Go function, you give a definition of what the function has to do. To use a function, you will have to call that function to perform the defined task.When a program calls a function, the program control is transferred to the called function. A called function performs a defined task and when its return statement is executed or when its function-ending closing brace is reached, it returns the program control back to the main program.

package main
import "fmt"

func main() {
    /* local variable definition */
    var a int = 300
    var b int = 200
    var ret int

    /* calling a function to get max value */
    ret = max(a, b)

    fmt.Printf( "Max value is : %d\n", ret )
}

/* function returning the max between two productbers */
func max(product1, product2 int) int {
    /* local variable declaration */
    var result int

    if (product1 > product2) {
        result = product1
    } else {
        result = product2
    }
    return result
}
We have kept the max() function along with the main() function and compiled the source code. While running the final executable, it would produce the following result
$go run main.go
Max value is : 300

Returning multiple values from Function

A Go function can return multiple values. For example
package main

import "fmt"

func swap(x, y string) (string, string) {
   return y, x
}
func main() {
   a, b := swap("India", "Summar")
   fmt.Println(a, b)
}
When the above code is compiled and executed, it produces the following result -
$go run main.go
Summar India

Function Arguments

If a function is to use arguments, it must declare variables that accept the values of the arguments. These variables are called the formal parameters of the function. While calling a function, there are two ways that arguments can be passed to a function-
Sr.No Call Type & Description
1 Call by value

This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument.

2 Call by reference

This method copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument.

Function Usage

A function can be used in the following ways:

Sr.No Function Usage & Description
1 Function as Value

Functions can be created on the fly and can be used as values.

2 Function Closures

Functions closures are anonymous functions and can be used in dynamic programming.

3 Method

Methods are special functions with a receiver.