Downloading and Storing Package Code

In addition to the package name, Go programs that want to import your package 0:01 will need to know its package path. 0:04 The package path is decided by what directory you store your package code in. 0:06 The Go workspace directory is a folder on your computer where all of 0:10 your Go code should be stored. 0:13 The Go workspace is not the same thing as Treehouse workspaces. 0:15 Sorry if that's a little confusing. 0:19 By default, the Go workspace will be a go sub directory in your user's 0:21 home directory, but you can change this using the GOPATH environment variable. 0:25 So let's take a look what GOPATH is set to here in this workspace. 0:32 Here in treehouse/workspaces, 0:35 GOPATH is setup to point to the workspace subdirectory. 0:37 Go code should go in a source subdirectory within the workspace, and 0:41 then you should create a subdirectory for the each segment of the package path. 0:44 We've set this package under github.com/treehouse-projects/go-intro and 0:47 then the welcome package. 0:54 We'll explain why we use such a detailed package path shortly. 0:56 Let's create a Go program that uses this package. 1:00 To import a package into a go file, 1:03 you'll use the package path, followed by the package name. 1:05 So let's go here into our temp.go file, and as always, this is going 1:08 to run from the command line, so we're going to put this in the main package. 1:13 And then we'll do an import statement. 1:17 We're gonna import a couple different packages here. 1:18 So we'll use the multi-package form of the import command. 1:23 First we'll import the format packet so that we can use the print line function. 1:29 And then we'll import our welcome package. 1:34 To do that, we're going to leave the source directory off, 1:38 that's always assumed by default. 1:41 But we'll start with 1:43 github.com/treehouse-projects/go-intro/ 1:44 and that's the import path, and now we need the name of the actual package. 1:55 That'll be the last segment of our import string. 2:01 So we'll use the welcome package name. 2:07 I never actually used the contents that we imported from that package, so 2:11 we'll create a main function here which will run when our program does. 2:15 And we're gonna call the Println function, and 2:20 we'll just pass it some of the constants from the welcome package. 2:24 So since these constants are coming from another package, 2:31 we need to qualify it using the package name, so we'll say welcome., 2:35 and then we'll say the name of our English constant. 2:40 Remember, that starts with a capital letter because it's exported. 2:44 And then we'll just copy this and, Print out the Japanese welcome as well. 2:48 Save that, now let's try running it. 2:59 go run temp.go, 3:02 and it prints out our two welcomes, the first in English, second in Japanese. 3:05 Now, what if we were to try to use the unexported constant though? 3:11 So, let's try adding a third Println call. 3:16 And this time, we're going to try to access the welcome packages 3:21 klingon, Constant. 3:26 But remember, this is an unexported constant, 3:30 because it begins with a lowercase letter. 3:33 Let's try running this. You see, this time it refuses to compile. 3:36 It can't refer to an unexported name, welcome.klingon. 3:41 That means that the klingon constant can only be used within the welcome package. 3:45 It can't be used from outside it. 3:49 We can also download packages from the web and install them on our system for 3:52 our go programs to use. 3:56 So for example, the golang team here has an example 3:57 repository which includes a stringutil package that our programs can use. 4:02 So here within the stringutil package I can look in the reverse.go source file and 4:07 see that there's a reverse function that I'd like to try using in a package. 4:14 So let's try writing a program that uses that. 4:18 So I'm gonna import that package, 4:21 which has a package path of 4:26 github.com/golang/example/stringutil. 4:30 stringutil is the package name, and 4:38 everything preceding that is the package path. 4:39 Once I've imported that package, then I no longer need to use the full package path, 4:43 I can just say string, I can just use the package name, stringutil.Reverse. 4:48 And I pass it the string that I'd like it to reverse for me. 4:58 So the return value of this would be the string that I passed to it backwards. 5:03 Let's just print that result out. 5:08 fmt.Println. 5:10 Hello reversed. 5:14 Now if we try to go run temp.go right now, we'll get an error. 5:16 Cannot find packet, github.com/golang/example/stringutil. 5:21 So first, we'll use the go command's get subcommand to download and 5:26 install the package we need. 5:30 So I'll just copy and paste the package path and 5:32 package name right out of my code down here into the console. 5:35 And I'll run the get subcommand of the go command and paste that right here. 5:39 The go get command sees that the library package path starts with github.com. 5:49 That has no meaning to the go language, but go get knows that GitHub is a site 5:55 that hosts git repositories that it can clone the package code from. 6:00 So go get downloads the package from GitHub for us. 6:04 Now let me refresh our file tree so 6:07 that I can show you what changes go get made over here. 6:10 go get will create a source subdirectory in your Go workspace directory, 6:13 if it doesn't already exist. 6:17 And then it'll create subdirectories for each segment of the package path. 6:19 So github.com/golang/example/ and 6:22 then the stringutil package. 6:28 The github.com/go/example repo also contains several other packages. 6:32 And go get just clones the whole repo at once. 6:37 Now that the stringutil package is installed, we can try rerunning temp.go. 6:39 So we'll go back to our console. 6:44 And type go run temp.go. 6:45 And this time the package will be found. 6:52 The program will run successfully, and we'll see our reverse string as output. 6:54