What is it

func HelloWorld() string {
  return "Hello World"
}

• Function name of HelloWorld
• returns string type

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

• Defines a function of name add
• Defines Params
  • accept parameter of x which is of type int
  • accept parameter of y which is also of type int
• Defines Return type
  • function returns type of int

Result parameter and Return

The result parameter acts as an ordinary local variable and the function may assign values to them after instantiation using return.

• Regardless of how result parameters are declared, all the result values are initialized to the zero values for their type upon entry to the function.

A return statement that specifies results sets the result parameters before any deferred functions are executed.

• see defer section.

When you have multiple return values in a function, result parameter must be wrapped in a parenthesis ().

func twoReturns() (r1 string, r2 string) {
  // ...
}

Void return

In Go, returning nothing is implicit when no result parameter is defined.

// Valid function with no return value
func sayHello(name string) {
  fmt.Println("Hello,", name)
}

Error Handling Convention

When a function returns a err as second return value, you can use it to catch error.

// package.method() has two return values
result, err := package.method()

if err != nil {
  log.Printf("error calling package.method: %v", err)
}