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remove print() from the tutorial, generating a little clumsiness around "import"

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R=rsc,gri
DELTA=103  (36 added, 33 deleted, 34 changed)
OCL=26442
CL=26491
This commit is contained in:
Rob Pike 2009-03-18 14:09:16 -07:00
parent 08eeb2535d
commit bdbb3b455e
15 changed files with 70 additions and 75 deletions
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58
doc/go_tutorial.txt
View File

@ -4,7 +4,7 @@ Let's Go
Rob Pike
----
(March 17, 2009)
(March 18, 2009)
This document is a tutorial introduction to the basics of the Go systems programming
@ -36,7 +36,9 @@ Let's start in the usual way:
Every Go source file declares, using a "package" statement, which package it's part of.
The "main" package's "main" function is where the program starts running (after
any initialization).
any initialization). It may also import other packages to use their facilities.
This program imports the package "fmt" to gain access to
our old, now capitalized and package-qualified friend, "fmt.Printf".
Function declarations are introduced with the "func" keyword.
@ -44,18 +46,6 @@ Notice that string constants can contain Unicode characters, encoded in UTF-8.
Go is defined to accept UTF-8 input. Strings are arrays of bytes, usually used
to store Unicode strings represented in UTF-8.
The built-in function "print()" has been used during the early stages of
development of the language but is not guaranteed to last. Here's a version of the
program that doesn't depend on "print()":
--PROG progs/helloworld2.go
This version imports the ''os'' package to acess its "Stdout" variable, of type
"*os.File". The "import" statement is a declaration: it names the identifier ("os")
that will be used to access members of the package imported from the file ("os"),
found in the current directory or in a standard location.
Given "os.Stdout" we can use its "WriteString" method to print the string.
The comment convention is the same as in C++:
/* ... */
@ -84,12 +74,23 @@ Semicolons aren't needed here; in fact, semicolons are unnecessary after any
top-level declaration, even though they are needed as separators <i>within</i>
a parenthesized list of declarations.
Also notice that we've dropped the explicit name from the imports; by default,
This program imports the "&quot;os&quot;" package to access its "Stdout" variable, of type
"*os.File". The "import" statement is actually a declaration: in its general form,
as used in our ``hello world'' program,
it names the identifier ("fmt")
that will be used to access members of the package imported from the file ("&quot;fmt&quot;"),
found in the current directory or in a standard location.
In this program, though, we've dropped the explicit name from the imports; by default,
packages are imported using the name defined by the imported package,
which by convention is of course the file name itself. You can specify your
which by convention is of course the file name itself. Our ``hello world'' program
could have said just "import &quot;fmt&quot;".
You can specify your
own import names if you want but it's only necessary if you need to resolve
a naming conflict.
Given "os.Stdout" we can use its "WriteString" method to print the string.
Having imported the "flag" package, line 8 creates a global variable to hold
the value of echo's "-n" flag. The variable "n_flag" has type "*bool", pointer
to "bool".
@ -407,7 +408,7 @@ Finally, we can use our new package:
--PROG progs/helloworld3.go
and run the program:
And now we can run the program:
% helloworld3
hello, world
@ -424,8 +425,8 @@ Building on the "file" package, here's a simple version of the Unix utility "cat
By now this should be easy to follow, but the "switch" statement introduces some
new features. Like a "for" loop, an "if" or "switch" can include an
initialization statement. The "switch" on line 12 uses one to create variables
"nr" and "er" to hold the return values from "f.Read()". (The "if" on line 19
initialization statement. The "switch" on line 14 uses one to create variables
"nr" and "er" to hold the return values from "f.Read()". (The "if" on line 21
has the same idea.) The "switch" statement is general: it evaluates the cases
from top to bottom looking for the first case that matches the value; the
case expressions don't need to be constants or even integers, as long as
@ -437,7 +438,7 @@ in a "for" statement, a missing value means "true". In fact, such a "switch"
is a form of "if-else" chain. While we're here, it should be mentioned that in
"switch" statements each "case" has an implicit "break".
Line 19 calls "Write()" by slicing the incoming buffer, which is itself a slice.
Line 21 calls "Write()" by slicing the incoming buffer, which is itself a slice.
Slices provide the standard Go way to handle I/O buffers.
Now let's make a variant of "cat" that optionally does "rot13" on its input.
@ -462,7 +463,7 @@ we have a second implementation of the "reader" interface.
--PROG progs/cat_rot13.go /type.rotate13/ /end.of.rotate13/
(The "rot13" function called on line 37 is trivial and not worth reproducing.)
(The "rot13" function called on line 38 is trivial and not worth reproducing.)
To use the new feature, we define a flag:
@ -474,7 +475,7 @@ and use it from within a mostly unchanged "cat()" function:
(We could also do the wrapping in "main" and leave "cat()" mostly alone, except
for changing the type of the argument; consider that an exercise.)
Lines 51 through 53 set it all up: If the "rot13" flag is true, wrap the "reader"
Lines 52 through 55 set it all up: If the "rot13" flag is true, wrap the "reader"
we received into a "rotate13" and proceed. Note that the interface variables
are values, not pointers: the argument is of type "reader", not "*reader",
even though under the covers it holds a pointer to a "struct".
@ -551,11 +552,8 @@ Printing
The examples of formatted printing so far have been modest. In this section
we'll talk about how formatted I/O can be done well in Go.
There's a package "fmt" that implements a version of "Printf" (upper case)
that should look familiar:
--PROG progs/printf.go
We've seen simple uses of the package "fmt", which
implements "Printf", "Fprintf", and so on.
Within the "fmt" package, "Printf" is declared with this signature:
Printf(format string, v ...) (n int, errno *os.Error)
@ -740,7 +738,7 @@ together:
--PROG progs/sieve.go /func.main/ /^}/
Line 23 creates the initial channel to pass to "generate", which it
Line 25 creates the initial channel to pass to "generate", which it
then starts up. As each prime pops out of the channel, a new "filter"
is added to the pipeline and <i>its</i> output becomes the new value
of "ch".
@ -756,7 +754,7 @@ channel, launches a goroutine internally using a function literal, and
returns the channel to the caller. It is a factory for concurrent
execution, starting the goroutine and returning its connection.
The function literal notation (lines 6-10) allows us to construct an
The function literal notation (lines 8-12) allows us to construct an
anonymous function and invoke it on the spot.
The same change can be made to "filter":
@ -789,7 +787,7 @@ code that invokes the operation and responds to the request:
--PROG progs/server.go /type.binOp/ /^}/
Line 8 defines the name "binOp" to be a function taking two integers and
Line 10 defines the name "binOp" to be a function taking two integers and
returning a third.
The "server" routine loops forever, receiving requests and, to avoid blocking due to

8
doc/progs/cat.go
View File

@ -7,6 +7,8 @@ package main
import (
"file";
"flag";
"fmt";
"os";
)
func cat(f *file.File) {
@ -15,13 +17,13 @@ func cat(f *file.File) {
for {
switch nr, er := f.Read(buf); true {
case nr < 0:
print("error reading from ", f.String(), ": ", er.String(), "\n");
fmt.Fprintf(os.Stderr, "error reading from %s: %s\n", f.String(), er.String());
sys.Exit(1);
case nr == 0: // EOF
return;
case nr > 0:
if nw, ew := file.Stdout.Write(buf[0:nr]); nw != nr {
print("error writing from ", f.String(), ": ", ew.String(), "\n");
fmt.Fprintf(os.Stderr, "error writing from %s: %s\n", f.String(), ew.String());
}
}
}
@ -35,7 +37,7 @@ func main() {
for i := 0; i < flag.NArg(); i++ {
f, err := file.Open(flag.Arg(i), 0, 0);
if f == nil {
print("can't open ", flag.Arg(i), ": error ", err, "\n");
fmt.Fprintf(os.Stderr, "can't open %s: error %s\n", flag.Arg(i), err);
sys.Exit(1);
}
cat(f);

7
doc/progs/cat_rot13.go
View File

@ -7,6 +7,7 @@ package main
import (
"file";
"flag";
"fmt";
"os";
)
@ -58,14 +59,14 @@ func cat(r reader) {
for {
switch nr, er := r.Read(buf); {
case nr < 0:
print("error reading from ", r.String(), ": ", er.String(), "\n");
fmt.Fprintf(os.Stderr, "error reading from %s: %s\n", r.String(), er.String());
sys.Exit(1);
case nr == 0: // EOF
return;
case nr > 0:
nw, ew := file.Stdout.Write(buf[0:nr]);
if nw != nr {
print("error writing from ", r.String(), ": ", ew.String(), "\n");
fmt.Fprintf(os.Stderr, "error writing from %s: %s\n", r.String(), ew.String());
}
}
}
@ -79,7 +80,7 @@ func main() {
for i := 0; i < flag.NArg(); i++ {
f, err := file.Open(flag.Arg(i), 0, 0);
if f == nil {
print("can't open ", flag.Arg(i), ": error ", err, "\n");
fmt.Fprintf(os.Stderr, "can't open %s: error %s\n", flag.Arg(i), err);
sys.Exit(1);
}
cat(f);

4
doc/progs/helloworld.go
View File

@ -4,6 +4,8 @@
package main
import fmt "fmt" // Package implementing formatted I/O.
func main() {
print("Hello, world; or Καλημέρα κόσμε; or こんにちは 世界\n");
fmt.Printf("Hello, world; or Καλημέρα κόσμε; or こんにちは 世界\n");
}

11
doc/progs/helloworld2.go
View File

@ -1,11 +0,0 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import os "os" // this package contains features for basic I/O
func main() {
os.Stdout.WriteString("Hello, world; or Καλημέρα κόσμε; or こんにちは 世界\n");
}

7
doc/progs/helloworld3.go
View File

@ -4,14 +4,17 @@
package main
import file "file"
import (
"file";
"fmt";
)
func main() {
hello := []byte{'h', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd', '\n'};
file.Stdout.Write(hello);
file, err := file.Open("/does/not/exist", 0, 0);
if file == nil {
print("can't open file; err=", err.String(), "\n");
fmt.Printf("can't open file; err=%s\n", err.String());
sys.Exit(1);
}
}

11
doc/progs/printf.go
View File

@ -1,11 +0,0 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import "fmt"
func main() {
fmt.Printf("hello, %s\n", "world");
}

4
doc/progs/run
View File

@ -8,7 +8,6 @@ rm -f *.6
for i in \
file.go \
helloworld.go \
helloworld2.go \
helloworld3.go \
echo.go \
cat.go \
@ -17,7 +16,6 @@ for i in \
sort.go \
sortmain.go \
print.go \
printf.go \
print_string.go \
sieve.go \
sieve1.go \
@ -48,7 +46,6 @@ function testitpipe {
testit helloworld "" "Hello, world; or Καλημέρα κόσμε; or こんにちは 世界"
testit helloworld2 "" "Hello, world; or Καλημέρα κόσμε; or こんにちは 世界"
testit helloworld3 "" "hello, world can't open file; err=No such file or directory"
testit echo "hello, world" "hello, world"
testit sum "" "6"
@ -62,7 +59,6 @@ echo $rot13 | testit cat_rot13 "--rot13" $alphabet
testit sortmain "" "Sunday Monday Tuesday Thursday Friday"
testit print "" "18446744073709551615 -1 18446744073709551615 {77 Sunset Strip} [1 2 3 4] 18446744073709551615 {77 Sunset Strip} [1 2 3 4] 18446744073709551615 {77 Sunset Strip} [1 2 3 4]"
testit printf "" "hello, world"
testit print_string "" "77 Sunset Strip"
testitpipe sieve "sed 10q" "2 3 5 7 11 13 17 19 23 29"

6
doc/progs/server.go
View File

@ -4,6 +4,8 @@
package main
import "fmt"
type request struct {
a, b int;
replyc chan int;
@ -42,8 +44,8 @@ func main() {
}
for i := N-1; i >= 0; i-- { // doesn't matter what order
if <-reqs[i].replyc != N + 2*i {
print("fail at ", i, "\n");
fmt.Println("fail at", i);
}
}
print("done\n");
fmt.Println("done");
}

4
doc/progs/server1.go
View File

@ -4,6 +4,8 @@
package main
import "fmt"
type request struct {
a, b int;
replyc chan int;
@ -47,7 +49,7 @@ func main() {
}
for i := N-1; i >= 0; i-- { // doesn't matter what order
if <-reqs[i].replyc != N + 2*i {
print("fail at ", i, "\n");
fmt.Println("fail at", i);
}
}
quit <- true;

4
doc/progs/sieve.go
View File

@ -4,6 +4,8 @@
package main
import "fmt"
// Send the sequence 2, 3, 4, ... to channel 'ch'.
func generate(ch chan int) {
for i := 2; ; i++ {
@ -28,7 +30,7 @@ func main() {
go generate(ch); // Start generate() as a goroutine.
for {
prime := <-ch;
print(prime, "\n");
fmt.Println(prime);
ch1 := make(chan int);
go filter(ch, ch1, prime);
ch = ch1

4
doc/progs/sieve1.go
View File

@ -4,6 +4,8 @@
package main
import "fmt"
// Send the sequence 2, 3, 4, ... to returned channel
func generate() chan int {
ch := make(chan int);
@ -44,6 +46,6 @@ func sieve() chan int {
func main() {
primes := sieve();
for {
print(<-primes, "\n");
fmt.Println(<-primes);
}
}

9
doc/progs/sortmain.go
View File

@ -4,7 +4,10 @@
package main
import "sort"
import (
"fmt";
"sort";
)
func ints() {
data := []int{74, 59, 238, -784, 9845, 959, 905, 0, 0, 42, 7586, -5467984, 7586};
@ -53,9 +56,9 @@ func days() {
panic()
}
for i, d := range data {
print(d.long_name, " ")
fmt.Printf("%s ", d.long_name)
}
print("\n")
fmt.Printf("\n")
}

4
doc/progs/strings.go
View File

@ -4,9 +4,11 @@
package main
import "fmt"
func main() {
s := "hello";
if s[1] == 'e' { print("success") }
if s[1] != 'e' { sys.Exit(1) }
s = "good bye";
var p *string = &s;
*p = "ciao";

4
doc/progs/sum.go
View File

@ -4,6 +4,8 @@
package main
import "fmt"
func sum(a []int) int { // returns an int
s := 0;
for i := 0; i < len(a); i++ {
@ -15,5 +17,5 @@ func sum(a []int) int { // returns an int
func main() {
s := sum([3]int{1,2,3}); // a slice of the array is passed to sum
print(s, "\n");
fmt.Print(s, "\n");
}