diff options
Diffstat (limited to 'doc/articles/defer_panic_recover.html')
| -rw-r--r-- | doc/articles/defer_panic_recover.html | 94 |
1 files changed, 8 insertions, 86 deletions
diff --git a/doc/articles/defer_panic_recover.html b/doc/articles/defer_panic_recover.html index be97045dd..206b836d8 100644 --- a/doc/articles/defer_panic_recover.html +++ b/doc/articles/defer_panic_recover.html @@ -1,10 +1,7 @@ <!--{ - "Title": "Defer, Panic, and Recover" + "Title": "Defer, Panic, and Recover", + "Template": true }--> -<!-- - DO NOT EDIT: created by - tmpltohtml articles/defer_panic_recover.tmpl ---> <p> Go has the usual mechanisms for control flow: if, for, switch, goto. It also @@ -23,23 +20,7 @@ For example, let's look at a function that opens two files and copies the contents of one file to the other: </p> -<pre><!--{{code "progs/defer.go" `/func CopyFile/` `/STOP/`}} --->func CopyFile(dstName, srcName string) (written int64, err error) { - src, err := os.Open(srcName) - if err != nil { - return - } - - dst, err := os.Create(dstName) - if err != nil { - return - } - - written, err = io.Copy(dst, src) - dst.Close() - src.Close() - return -}</pre> +{{code "/doc/progs/defer.go" `/func CopyFile/` `/STOP/`}} <p> This works, but there is a bug. If the call to os.Create fails, the @@ -50,22 +31,7 @@ noticed and resolved. By introducing defer statements we can ensure that the files are always closed: </p> -<pre><!--{{code "progs/defer2.go" `/func CopyFile/` `/STOP/`}} --->func CopyFile(dstName, srcName string) (written int64, err error) { - src, err := os.Open(srcName) - if err != nil { - return - } - defer src.Close() - - dst, err := os.Create(dstName) - if err != nil { - return - } - defer dst.Close() - - return io.Copy(dst, src) -}</pre> +{{code "/doc/progs/defer2.go" `/func CopyFile/` `/STOP/`}} <p> Defer statements allow us to think about closing each file right after opening @@ -88,13 +54,7 @@ In this example, the expression "i" is evaluated when the Println call is deferred. The deferred call will print "0" after the function returns. </p> -<pre><!--{{code "progs/defer.go" `/func a/` `/STOP/`}} --->func a() { - i := 0 - defer fmt.Println(i) - i++ - return -}</pre> +{{code "/doc/progs/defer.go" `/func a/` `/STOP/`}} <p> 2. <i>Deferred function calls are executed in Last In First Out order @@ -105,12 +65,7 @@ deferred. The deferred call will print "0" after the function returns. This function prints "3210": </p> -<pre><!--{{code "progs/defer.go" `/func b/` `/STOP/`}} --->func b() { - for i := 0; i < 4; i++ { - defer fmt.Print(i) - } -}</pre> +{{code "/doc/progs/defer.go" `/func b/` `/STOP/`}} <p> 3. <i>Deferred functions may read and assign to the returning function's named @@ -122,11 +77,7 @@ In this example, a deferred function increments the return value i <i>after</i> the surrounding function returns. Thus, this function returns 2: </p> -<pre><!--{{code "progs/defer.go" `/func c/` `/STOP/`}} --->func c() (i int) { - defer func() { i++ }() - return 1 -}</pre> +{{code "/doc/progs/defer.go" `/func c/` `/STOP/`}} <p> This is convenient for modifying the error return value of a function; we will @@ -156,36 +107,7 @@ to panic and resume normal execution. Here's an example program that demonstrates the mechanics of panic and defer: </p> -<pre><!--{{code "progs/defer2.go" `/package main/` `/STOP/`}} --->package main - -import "fmt" - -func main() { - f() - fmt.Println("Returned normally from f.") -} - -func f() { - defer func() { - if r := recover(); r != nil { - fmt.Println("Recovered in f", r) - } - }() - fmt.Println("Calling g.") - g(0) - fmt.Println("Returned normally from g.") -} - -func g(i int) { - if i > 3 { - fmt.Println("Panicking!") - panic(fmt.Sprintf("%v", i)) - } - defer fmt.Println("Defer in g", i) - fmt.Println("Printing in g", i) - g(i + 1) -}</pre> +{{code "/doc/progs/defer2.go" `/package main/` `/STOP/`}} <p> The function g takes the int i, and panics if i is greater than 3, or else it |