io: simplify Examples

- CopyN: 5 creates ambiguity with respect to whitespace and upperbound
- TeeReader less boilerplate and displays a common usage of it
- SectionReader_* all sections unified to 5:17 for clarity
- SectionReader_Seek uses io.Copy to stdout like other examples
- Seeker_Seek remove useless prints
- Pipe print reader like other examples

Updates #36417

Change-Id: Ibd01761d5a5786cdb1ea934f7a98f8302430c8a5
GitHub-Last-Rev: 4c17f9a8e32d89743b7eaec7c52032256972cc0a
GitHub-Pull-Request: golang/go#38379
Reviewed-on: https://go-review.googlesource.com/c/go/+/227868
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/io/example_test.go b/src/io/example_test.go
index 2eaab678c9f613b8aed47b70d910d00ecd542973..465eed4d5e4cf718943ca9c631160cfc87137efd 100644 (file)
--- a/src/io/example_test.go
+++ b/src/io/example_test.go
@@ -48,7 +48,7 @@ func ExampleCopyBuffer() {
 func ExampleCopyN() {
        r := strings.NewReader("some io.Reader stream to be read")
 
-       if _, err := io.CopyN(os.Stdout, r, 5); err != nil {
+       if _, err := io.CopyN(os.Stdout, r, 4); err != nil {
                log.Fatal(err)
        }
 
@@ -136,25 +136,15 @@ func ExampleMultiReader() {
 }
 
 func ExampleTeeReader() {
-       r := strings.NewReader("some io.Reader stream to be read\n")
-       var buf bytes.Buffer
-       tee := io.TeeReader(r, &buf)
-
-       printall := func(r io.Reader) {
-               b, err := ioutil.ReadAll(r)
-               if err != nil {
-                       log.Fatal(err)
-               }
+       var r io.Reader = strings.NewReader("some io.Reader stream to be read\n")
 
-               fmt.Printf("%s", b)
-       }
+       r = io.TeeReader(r, os.Stdout)
 
-       printall(tee)
-       printall(&buf)
+       // Everything read from r will be copied to stdout.
+       ioutil.ReadAll(r)
 
        // Output:
        // some io.Reader stream to be read
-       // some io.Reader stream to be read
 }
 
 func ExampleSectionReader() {
@@ -171,7 +161,7 @@ func ExampleSectionReader() {
 
 func ExampleSectionReader_ReadAt() {
        r := strings.NewReader("some io.Reader stream to be read\n")
-       s := io.NewSectionReader(r, 5, 16)
+       s := io.NewSectionReader(r, 5, 17)
 
        buf := make([]byte, 6)
        if _, err := s.ReadAt(buf, 10); err != nil {
@@ -186,30 +176,24 @@ func ExampleSectionReader_ReadAt() {
 
 func ExampleSectionReader_Seek() {
        r := strings.NewReader("some io.Reader stream to be read\n")
-       s := io.NewSectionReader(r, 5, 16)
+       s := io.NewSectionReader(r, 5, 17)
 
        if _, err := s.Seek(10, io.SeekStart); err != nil {
                log.Fatal(err)
        }
 
-       buf := make([]byte, 6)
-       if _, err := s.Read(buf); err != nil {
+       if _, err := io.Copy(os.Stdout, s); err != nil {
                log.Fatal(err)
        }
 
-       fmt.Printf("%s\n", buf)
-
        // Output:
        // stream
 }
 
 func ExampleSeeker_Seek() {
        r := strings.NewReader("some io.Reader stream to be read\n")
-       if _, err := io.Copy(os.Stdout, r); err != nil {
-               log.Fatal(err)
-       }
 
-       r.Seek(15, io.SeekStart)
+       r.Seek(5, io.SeekStart) // move to the 5th char from the start
        if _, err := io.Copy(os.Stdout, r); err != nil {
                log.Fatal(err)
        }
@@ -220,8 +204,7 @@ func ExampleSeeker_Seek() {
        }
 
        // Output:
-       // some io.Reader stream to be read
-       // stream to be read
+       // io.Reader stream to be read
        // read
 }
 
@@ -247,14 +230,14 @@ func ExamplePipe() {
        r, w := io.Pipe()
 
        go func() {
-               fmt.Fprint(w, "some text to be read\n")
+               fmt.Fprint(w, "some io.Reader stream to be read\n")
                w.Close()
        }()
 
-       buf := new(bytes.Buffer)
-       buf.ReadFrom(r)
-       fmt.Print(buf.String())
+       if _, err := io.Copy(os.Stdout, r); err != nil {
+               log.Fatal(err)
+       }
 
        // Output:
-       // some text to be read
+       // some io.Reader stream to be read
 }