ch04-functions.md

Functions

We have already used functions in form of the main function using the func keyword.

Format:

func awesomeFunction() { // Notice the same line curly brace, its a mandatory formatting rule to have it like that.
      <cool stuffs>
}

We can specify the function arguments like:

func awesomeFunction(arg1 string, arg2 int, arg3 float32) { 
      <cool stuffs>
}

Declaring multiple same datatype arguments:

func awesomeFunction(arg1, arg2 string) { 
      <cool stuffs>
}

or:

func awesomeFunction(arg1 ...string) { // 
      <cool stuffs>
}

Using function return values:

func awesomeFunction() error {
      // Notice that it is not mandatory to specify the return value name but we can still specify one if we wish, in which case it would be
      // returned implicitly.
      <cool stuffs>

      return err
}

In Go, we are not bound to return just a single value but instead, we can even return multiple values from a function

func awesomeFunction() (someNumber int, e error) {
      <cool stuffs>

      return // someNumber and e will be returned implicitly.
}

Defer

The keyword defer can be used to perform any certain operation that we wish to perform before the function exit. This is specially useful for doing things like closing opened resources such as a file or open connections such as to a socket file.

We can have multiple defer in a single function, they work by FILO(First In Last Out) so the first defer you define in the function will always be executed as the last operation of the function.

Example:

func awesomeFunction() {
      defer fmt.Printf("Final Goodbye.") // this will be executed last.
      defer fmt.Printf("Just Kidding..\n")
      defer fmt.Printf("Goodbye.\n") // this will run as the first defer.
}

The output of above will be as:

Goodbye.
Just Kidding
Final Goodbye.

Must Read Don’t defer Close() on writable files