Go (golang) Tutorials - Custom Packages and Functions

Published: 12 March 2018
on channel: Ambasoft Java

1,759

#golang #go #packages

Custom Packages and Functions
-----------------------------
A. Blank identifier - _ "underscore"
B. Godoc - Utility to get package documentation about all the go packages
C. Returning values from functions - User defined functions
D. Custom packages
Note:-
Function names starts with lowercase alphabets will not be exported to use outside from a go program
Function names started with uppercase letters are only can be used outside the go program or package
1. Set up GOPATH to the current working directory/ root of the package
2. Inside GOPATH directory create src/packagename ex:- GOPATH/src/hello - Hello is the name of the package
3. Create Package Hello (not a command)
4. Switch over to the GOPATH directory
5. Create a go program to import and use the custom package hello

Source Code
---------------

blankdemo.go
--------------
package main
import ("fmt"
_ "strings"
)
func main(){
fmt.Println("Blank demo")
}

funcdemo.go
-------------
package main
import "fmt"

func main(){
show() //Call Function Show
display("Calling display with argument")
result:=add(10,20)
fmt.Printf("The sum is %d\n",result)
}
func show(){
fmt.Println("Inside Show Function")
}
func display(message string){
fmt.Println(message)
}
func add(first int,second int)(int){ //Return values from the function
sum:=first+second
return sum
}

mathematics.go (create it inside GOPATH/src/mathematics/)
-------------

package mathematics
func Add(a int,b int)(int){
return a+b
}
func Sub(a int,b int)(int){
return a-b
}
func Mul(a int,b int)(int){
return a*b
}
func Div(a int,b int)(int){
return a/b
}

calc.go (create it inside GOPATH)
-------
package main
import ("mathematics"
"fmt"
)
func main(){
a:=20
b:=10
fmt.Printf("The sum of %d and %d is %d \n",a,b,mathematics.Add(a,b))
fmt.Printf("The difference of %d and %d is %d\n",a,b,mathematics.Sub(a,b))
fmt.Printf("The product of %d and %d is %d\n",a,b,mathematics.Mul(a,b))
fmt.Printf("The division of %d and %d is %d\n",a,b,mathematics.Div(a,b))
}

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