Merge pull request #22 from mmcgrana/idiomatic-line-filters

Idiomatic line filters

examples/line-filters/line-filters.go

@@ -8,18 +8,20 @@
 // pattern to write your own Go line filters.
 package main
 
-// Package `bufio` will help us read line-by-line.
-import "bufio"
-import "strings"
-import "os"
-import "io"
+import (
+    "bufio"
+    "fmt"
+    "io"
+    "os"
+    "strings"
+)
 
 func main() {
 
     // Wrapping the unbuffered `os.Stdin` with a buffered
     // reader gives us a convenient `ReadString` method
     // that we'll use to read input line-by-line.
-    in := bufio.NewReader(os.Stdin)
+    rdr := bufio.NewReader(os.Stdin)
     out := os.Stdout
 
     // `ReadString` returns the next string from the
@@ -27,24 +29,28 @@ func main() {
     // newline byte `'\n'` as our separator so we'll get
     // successive input lines.
     for {
-        inLine, err := in.ReadString('\n')
+        switch line, err := rdr.ReadString('\n'); err {
+
+        // If the read succeeded (the read `err` is nil),
+        // write out out the uppercased line. Check for an
+        // error on this write as we do on the read.
+        case nil:
+            ucl := strings.ToUpper(line)
+            if _, err = out.WriteString(ucl); err != nil {
+                fmt.Fprintln(os.Stderr, "error:", err)
+                os.Exit(1)
+            }
 
         // The `EOF` error is expected when we reach the
         // end of input, so exit gracefully in that case.
-        // Otherwise there's a problem.
-        if err == io.EOF {
-            return
-        }
-        if err != nil {
-            panic(err)
-        }
+        case io.EOF:
+            os.Exit(0)
 
-        // Write out the uppercased line, checking for an
-        // error on the write as we did on the read.
-        outLine := strings.ToUpper(inLine)
-        _, err = out.WriteString(outLine)
-        if err != nil {
-            panic(err)
+        // Otherwise there's a problem; print the
+        // error and exit with non-zero status.
+        default:
+            fmt.Fprintln(os.Stderr, "error:", err)
+            os.Exit(1)
         }
     }
 }