Party Robot

Packages

In Go an application is organized in packages. A package is a collection of source files located in the same folder. All source files in a folder must have the same package name at the top of the file. By convention packages are named to be the same as the folder they are located in.

package greeting

Go provides an extensive standard library of packages which you can use in your program using the import keyword. Standard library packages are imported using their name.

package greeting

import "fmt"

An imported package is then addressed with the package name:

world := "World"
fmt.Sprintf("Hello %s", world)

Go determines if an item can be called by code in other packages through how it is declared. To make a function, type, variable, constant or struct field externally visible (known as exported) the name must start with a capital letter.

package greeting

// Hello is a public function (callable from other packages).
func Hello(name string) string {
    return "Hello " + name
}

// hello is a private function (not callable from other packages).
func hello(name string) string {
    return "Hello " + name
}

String Formatting

Go provides an in-built package called fmt (format package) which offers a variety of functions to manipulate the format of input and output. The most commonly used function is Sprintf, which uses verbs like %s to interpolate values into a string and returns that string.

import "fmt"

food := "taco"
fmt.Sprintf("Bring me a %s", food)
// Returns: Bring me a taco

In Go floating point values are conveniently formatted with Sprintf's verbs: %g (compact representation), %e (exponent) or %f (non exponent). All three verbs allow the field's width and numeric position to be controlled.

import "fmt"

number := 4.3242
fmt.Sprintf("%.2f", number)
// Returns: 4.32

You can find a full list of available verbs in the format package documentation.

fmt contains other functions for working with strings, such as Println which simply prints the arguments it receives to the console and Printf which formats the input in the same way as Sprintf before printing it.