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Go Language Overview

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Packages

6:42 with Jay McGavren

A Go program is split into several libraries, called packages.

  • Each file begins with package declaration
    • Packages are often used to set up a library for other programs to use. But there's a special package that provides a starting point for Go programs to run: the main package.
  • import makes other package contents available for use in the current source file
  • Package contents
    • Variables, functions, and other things declared at package level will be accessible anywhere in the package.
    • Again, there's a special starting point for Go programs to run: the main function.
  • Using imported packages
    • To refer to names of variables/constants/functions in another package, need to qualify the name: fmt.Println, welcome.English.
    • No need to qualify names declared in current package
package main

// We'll be calling functions from these two packages.
// So we need to import them here.
// Note the parentheses: this syntax lets you import
// multiple packages at once.
import (
    "fmt"
    "math"
)

// Declare a variable that will be accessible throughout
// the current package.
var myNumber = 1.23

func main() {
    // Call the Ceil function from the "math" package.
    // Then, assign it to a variable. This is the "short
    // variable declaration" syntax, which we'll talk
    // about in the "Variables" video.
    roundedUp := math.Ceil(myNumber)
    // Call the Floor function from the "math" package.
    roundedDown := math.Floor(myNumber)
    // Call the Println function from the "fmt" package.
    fmt.Println(roundedUp, roundedDown)
}

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    Packages are often use to set up a library for other programs to use. 0:00
    But there's a special package that provides a starting program for 0:03
    Go programs to run, the main package. 0:05
    We see this here at the start of our hello Go sample program. 0:08
    Following the package declaration, each go file includes an import statement, 0:12
    which states the names of several other packages that it needs to import. 0:16
    Once you've imported a package, you can use functions, constants, variables, and 0:21
    other things of declares within your current file. 0:26
    Then following the import statement comes the actual package contents. 0:29

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