diff options
Diffstat (limited to '_content/doc/tutorial/call-module-code.html')
| -rw-r--r-- | _content/doc/tutorial/call-module-code.html | 237 |
1 files changed, 237 insertions, 0 deletions
diff --git a/_content/doc/tutorial/call-module-code.html b/_content/doc/tutorial/call-module-code.html new file mode 100644 index 00000000..b7f7649f --- /dev/null +++ b/_content/doc/tutorial/call-module-code.html @@ -0,0 +1,237 @@ +<!--{ + "Title": "Call your code from another module", + "Path": "/doc/tutorial/call-module-code" +}--> + +<p> + In the <a href="create-module.html">previous section</a>, you created a + <code>greetings</code> module. In this section, you'll write code to make + calls to the <code>Hello</code> function in the module you just wrote. You'll + write code you can execute as an application, and which calls code in the + <code>greetings</code> module. +</p> + +<aside class="Note"> + <strong>Note:</strong> This topic is part of a multi-part tutorial that begins + with <a href="create-module.html">Create a Go module</a>. +</aside> + +<ol> + <li> + Create a <code>hello</code> directory for your Go module source code. This + is where you'll write your caller. + + <p> + For example, if your current directory in the command prompt is the + greetings directory, you could use the following commands: + </p> + + <pre> +cd .. +mkdir hello +cd hello +</pre + > + </li> + + <li> + In your text editor (in the hello directory), create a file in which to + write your code and call it hello.go. + </li> + + <li> + Write code to call the <code>Hello</code> function, then print the + function's return value. + + <p> + To do that, paste the following code into hello.go. + </p> + + <pre> +package main + +import ( + "fmt" + + "example.com/greetings" +) + +func main() { + // Get a greeting message and print it. + message := greetings.Hello("Gladys") + fmt.Println(message) +} +</pre + > + + <p> + In this code, you: + </p> + + <ul> + <li> + Declare a <code>main</code> package. In Go, code executed as an + application must go in a <code>main</code> package. + </li> + <li> + Import two packages: <code>example.com/greetings</code> and + <code>fmt</code>. This gives your code access to functions in those + packages. Importing <code>example.com/greetings</code> (the package + contained in the module you created earlier) gives you access to the + <code>Hello</code> function. You also import <code>fmt</code>, with + functions for handling input and output text (such as printing text to + the console). + </li> + <li> + Get a greeting by calling the <code>greetings</code> package’s + <code>Hello</code> function. + </li> + </ul> + </li> + + <li> + Create a new module for this hello package. + + <p> + From the command line at the hello directory, run the + <code>go mod init</code> command, giving it the name of the module your + code will be in (here, just use "hello"). + </p> + + <pre> +$ go mod init hello +go: creating new go.mod: module hello +</pre + > + </li> + + <li> + Edit the <code>hello</code> module to use the unpublished greetings module. + + <p> + For production use, you’d publish your modules on a server, either inside + your company or on the internet, and the Go command will download them + from there. For now, you need to adapt the caller's module so it can find + the greetings code on your local file system. + </p> + + <p> + To do that, make a small change to <code>hello</code> module’s go.mod + file. + </p> + + <ol> + <li> + In the hello directory, open the go.mod file, change it so that it looks + like the following, and save the file. + + <pre> +module hello + +go 1.14 + +<ins>replace example.com/greetings => ../greetings</ins> +</pre> + + <p> + Here, the + <a href="https://golang.org/ref/mod#tmp_15" + ><code>replace</code> directive</a + > + tells Go to replace the module path (the URL + <code>example.com/greetings</code>) with a path you specify. In this + case, that's a greetings directory next to the hello directory. + </p> + </li> + + <li> + In the hello directory, run <code>go build</code> to make Go locate the + module and add it as a dependency to the go.mod file. + + <pre> +$ go build +go: found example.com/greetings in example.com/greetings v0.0.0-00010101000000-000000000000 +</pre + > + </li> + + <li> + Look at go.mod again to see the changes made by <code>go build</code>, + including the <code>require</code> directive Go added. + + <pre> +module hello + +go 1.14 + +replace example.com/greetings => ../greetings + +<ins>require example.com/greetings v0.0.0-00010101000000-000000000000</ins> +</pre> + + <p> + To build the module, Go found the local code in the ../greetings + directory, then added a + <a href="https://golang.org/ref/mod#tmp_13" + ><code>require</code> directive</a + > + to specify that <code>hello</code> is dependent on (requires) + <code>example.com/greetings</code>. You created this dependency when + you imported the <code>greetings</code> package (contained in the + greetings module) in hello.go. The <code>replace</code> directive + tells Go where to find the <code>greetings</code> module, because it + isn't published yet. + </p> + + <p> + To reference a published module, a go.mod file would omit the + <code>replace</code> directive and use a + <code>require</code> directive with a tagged version number at the + end. + </p> + + <pre>require example.com/greetings v1.1.0</pre> + </li> + </ol> + </li> + + <li> + In the <code>hello</code> directory, run the <code>hello</code> executable + (created by <code>go build</code>) to confirm that the code works. + <ul> + <li> + On Linux or Mac: + + <pre> +$ ./hello +Hi, Gladys. Welcome! +</pre + > + </li> + + <li> + On Windows: + + <pre> +$ hello.exe +Hi, Gladys. Welcome! +</pre + > + </li> + </ul> + </li> +</ol> + +<p> + Congrats! You've written two functioning modules. In the tutorial's + <a href="handle-errors.html">next topic</a>, you'll add some error handling. +</p> + +<p class="Navigation"> + <a class="Navigation-prev" href="create-module.html" + >< Create a Go module</a + > + <a class="Navigation-next" href="handle-errors.html" + >Return and handle an error ></a + > +</p> |