From 6ba27a496a089d0971c137a1a0632a9a10a3be22 Mon Sep 17 00:00:00 2001 From: Russ Cox Date: Fri, 12 Feb 2021 14:32:52 -0500 Subject: _content: move content/static/* to _content/* The extra level of hierarchy here is unnecessary and confusing. The directory is now _content so that any Go source files in our docs are not considered by commands like "go mod tidy" and "go test all". Change-Id: Ib6d7cb12920193798ee825155a8f8b33f16e60d8 Reviewed-on: https://go-review.googlesource.com/c/website/+/291691 Trust: Russ Cox Run-TryBot: Russ Cox TryBot-Result: Go Bot Reviewed-by: Dmitri Shuralyov --- _content/doc/tutorial/handle-errors.html | 188 +++++++++++++++++++++++++++++++ 1 file changed, 188 insertions(+) create mode 100644 _content/doc/tutorial/handle-errors.html (limited to '_content/doc/tutorial/handle-errors.html') diff --git a/_content/doc/tutorial/handle-errors.html b/_content/doc/tutorial/handle-errors.html new file mode 100644 index 00000000..4dfd4b13 --- /dev/null +++ b/_content/doc/tutorial/handle-errors.html @@ -0,0 +1,188 @@ + + +

+ Handling errors is an essential feature of solid code. In this section, you'll + add a bit of code to return an error from the greetings module, then handle it + in the caller. +

+ + + +
    +
  1. + In greetings/greetings.go, add the code highlighted below. + +

    + There's no sense sending a greeting back if you don't know who to greet. + Return an error to the caller if the name is empty. Copy the following + code into greetings.go and save the file. +

    + + 
    +package greetings
+
+import (
+    "errors"
+    "fmt"
+)
+
+// Hello returns a greeting for the named person.
+func Hello(name string) (string, error) {
+    // If no name was given, return an error with a message.
+    if name == "" {
+        return "", errors.New("empty name")
+    }
+
+    // If a name was received, return a value that embeds the name 
+    // in a greeting message.
+    message := fmt.Sprintf("Hi, %v. Welcome!", name)
+    return message, nil
+}
+
    + +

    + In this code, you: +

    + +
      +
    • + Change the function so that it returns two values: a + string and an error. Your caller will check + the second value to see if an error occurred. (Any Go function can + return multiple values.) +
      • +
    • + Import the Go standard library errors package so you can + use its + errors.New function. +
      • +
    • + Add an if statement to check for an invalid request (an + empty string where the name should be) and return an error if the + request is invalid. The errors.New function returns an + error with your message inside. +
      • +
    • + Add nil (meaning no error) as a second value in the + successful return. That way, the caller can see that the function + succeeded. +
      • +
    +
    2. + +
  2. + In your hello/hello.go file, handle the error now returned by the + Hello function, along with the non-error value. + +

    + Paste the following code into hello.go. +

    + + 
    +package main
+
+import (
+    "fmt"
+    "log"
+
+    "example.com/greetings"
+)
+
+func main() {
+    // Set properties of the predefined Logger, including
+    // the log entry prefix and a flag to disable printing
+    // the time, source file, and line number.
+    log.SetPrefix("greetings: ")
+    log.SetFlags(0)
+
+    // Request a greeting message.
+    message, err := greetings.Hello("")
+    // If an error was returned, print it to the console and
+    // exit the program.
+    if err != nil {
+        log.Fatal(err)
+    }
+
+    // If no error was returned, print the returned message
+    // to the console.
+    fmt.Println(message)
+}
+
    + +

    + In this code, you: +

    + +
      +
    • + Configure the + log package to + print the command name ("greetings: ") at the start of its log messages, + without a time stamp or source file information. +
      • +
    • + Assign both of the Hello return values, including the + error, to variables. +
      • +
    • + Change the Hello argument from Gladys’s name to an empty + string, so you can try out your error-handling code. +
      • +
    • + Look for a non-nil error value. There's no sense continuing + in this case. +
      • +
    • + Use the functions in the standard library's log package to + output error information. If you get an error, you use the + log package's + Fatal function + to print the error and stop the program. +
      • +
    +
    3. + +
  3. + At the command line in the hello directory, run hello.go to + confirm that the code works. + +

    + Now that you're passing in an empty name, you'll get an error. +

    + + 
    +$ go run hello.go
+greetings: empty name
+exit status 1
+
    +
    4. +
+ +

+ That's essentially how error handling in Go works: Return an error as a value + so the caller can check for it. It's pretty simple. In the tutorial's + next topic, you'll use a Go slice to return + a randomly-selected greeting. +

+ +

+ < Call your code from another module + Return a random greeting > +

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