Golang packages: Difference between revisions
From wikinotes
Line 94: | Line 94: | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
// names/name.go | |||
import "fmt" | import "fmt" | ||
Line 104: | Line 104: | ||
func init() { | func init() { | ||
name = "foo" | name = "foo" | ||
fmt.Println( | fmt.Println("imported the first time") | ||
} | } | ||
</syntaxhighlight> | </syntaxhighlight> | ||
</blockquote><!-- init function --> | </blockquote><!-- init function --> | ||
</blockquote><!-- Defining Packages --> | </blockquote><!-- Defining Packages --> |
Revision as of 02:04, 2 June 2022
Basics
- Packages are groups of related code.
- Exported functions are callable when a package is imported
- The
main
package is your program's entrypoint (ex. cli)
Imports
import "fmt" import ( "fmt" // builtin pkgs have no module-path prefix "golang.org/x/example/stringutil" // non-builtin pkgs have module-path prefix (incl. local sub-packages) )
Defining Packages
Anatomy
# project heirarchy myproject/ mypackage/ libfoo.go libbar.go main.go go.mod
myproject/go.mod
// go.mod module github.com/you/myproject go 1.18
myproject/main.go
// main.go package main import "github.com/you/myproject/mypackage" func main() { mypackage.PrintHi(); }
myproject/mypackage/libfoo.go
// mypackage/libfoo.go package mypackage import "fmt" func PrintHi() { fmt.Println("hi") }Exported Functions
TODO:
Needs much more detail, and confirmation. (ex. what about constants? classes?)
Only exported symbols are exposed when a package is imported.
- Exported symbols/variables are upper-cased.
init function
Each file within a package can define an
init
function.
This function is evaluated the first time the package is imported.// names/name.go import "fmt" package names var name string func init() { name = "foo" fmt.Println("imported the first time") }