The size of the array is part of its type; however, one can declare
-a slice variable, to which one can assign a pointer to
-any array
-with the same element type or—much more commonly—a slice
-expression of the form a[low : high], representing
-the subarray indexed by low through high-1.
-Slices look a lot like arrays but have
+a slice variable to hold a reference to any array, of any size,
+with the same element type.
+A slice
+expression has the form a[low : high], representing
+the internal array indexed from low through high-1; the resulting
+slice is indexed from 0 through high-low-1.
+In short, slices look a lot like arrays but with
no explicit size ([] vs. [10]) and they reference a segment of
-an underlying, often anonymous, regular array. Multiple slices
+an underlying, usually anonymous, regular array. Multiple slices
can share data if they represent pieces of the same array;
multiple arrays can never share data.
@@ -302,17 +303,28 @@ regular arrays; they're more flexible, have reference semantics, and are efficient. What they lack is the precise control of storage layout of a regular array; if you want to have a hundred elements of an array stored within your structure, you should use a regular -array. +array. To create one, use a compound value constructor—an +expression formed +from a type followed by a brace-bounded expression like this: +
+
+ [3]int{1,2,3}
+
+
+In this case the constructor builds an array of 3 ints.
When passing an array to a function, you almost always want
to declare the formal parameter to be a slice. When you call
-the function, take the address of the array and Go will
-create (efficiently) a slice reference and pass that.
+the function, slice the array to create
+(efficiently) a slice reference and pass that.
+By default, the lower and upper bounds of a slice match the
+ends of the existing object, so the concise notation [:]
+will slice the whole array.
Using slices one can write this function (from sum.go):
-09 func sum(a []int) int { // returns an int
+09 func sum(a []int) int { // returns an int
10 s := 0
11 for i := 0; i < len(a); i++ {
12 s += a[i]
@@ -321,32 +333,27 @@ Using slices one can write this function (from sum.go):
15 }
-and invoke it like this: -
-
-19 s := sum(&[3]int{1,2,3}) // a slice of the array is passed to sum
-
-
Note how the return type (int) is defined for sum() by stating it
after the parameter list.
-The expression [3]int{1,2,3}—a type followed by a
-brace-bounded
-expression—is a constructor for a value, in this case an array
-of 3 ints.
-Putting an &
-in front gives us the address of a unique instance of the value. We pass the
-pointer to sum() by (implicitly) promoting it to a slice.
+
+To call the function, we slice the array. This intricate call (we'll show +a simpler way in a moment) constructs +an array and slices it: +
+
+ s := sum([3]int{1,2,3}[:])
+
If you are creating a regular array but want the compiler to count the
elements for you, use ... as the array size:
- s := sum(&[...]int{1,2,3})
+ s := sum([...]int{1,2,3}[:])
-In practice, though, unless you're meticulous about storage layout within a
-data structure, a slice itself—using empty brackets and no
-&—is all you need:
+That's fussier than necessary, though.
+In practice, unless you're meticulous about storage layout within a
+data structure, a slice itself—using empty brackets with no size—is all you need:
s := sum([]int{1,2,3})
@@ -687,7 +694,7 @@ Building on the file package, here's a simple version of the Unix u
15 const NBUF = 512
16 var buf [NBUF]byte
17 for {
-18 switch nr, er := f.Read(&buf); true {
+18 switch nr, er := f.Read(buf[:]); true {
19 case nr < 0:
20 fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", f.String(), er.String())
21 os.Exit(1)
@@ -803,7 +810,7 @@ and use it from within a mostly unchanged cat() function:
57 r = newRotate13(r)
58 }
59 for {
-60 switch nr, er := r.Read(&buf); {
+60 switch nr, er := r.Read(buf[:]); {
61 case nr < 0:
62 fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", r.String(), er.String())
63 os.Exit(1)
diff --git a/doc/go_tutorial.txt b/doc/go_tutorial.txt
index bcea0db2b5..477199ac3c 100644
--- a/doc/go_tutorial.txt
+++ b/doc/go_tutorial.txt
@@ -227,14 +227,15 @@ In Go, since arrays are values, it's meaningful (and useful) to talk
about pointers to arrays.
The size of the array is part of its type; however, one can declare
-a slice variable, to which one can assign a pointer to
-any array
-with the same element type or—much more commonly—a slice
-expression of the form "a[low : high]", representing
-the subarray indexed by "low" through "high-1".
-Slices look a lot like arrays but have
+a slice variable to hold a reference to any array, of any size,
+with the same element type.
+A slice
+expression has the form "a[low : high]", representing
+the internal array indexed from "low" through "high-1"; the resulting
+slice is indexed from "0" through "high-low-1".
+In short, slices look a lot like arrays but with
no explicit size ("[]" vs. "[10]") and they reference a segment of
-an underlying, often anonymous, regular array. Multiple slices
+an underlying, usually anonymous, regular array. Multiple slices
can share data if they represent pieces of the same array;
multiple arrays can never share data.
@@ -243,39 +244,43 @@ regular arrays; they're more flexible, have reference semantics,
and are efficient. What they lack is the precise control of storage
layout of a regular array; if you want to have a hundred elements
of an array stored within your structure, you should use a regular
-array.
+array. To create one, use a compound value constructor—an
+expression formed
+from a type followed by a brace-bounded expression like this:
+
+ [3]int{1,2,3}
+
+In this case the constructor builds an array of 3 "ints".
When passing an array to a function, you almost always want
to declare the formal parameter to be a slice. When you call
-the function, take the address of the array and Go will
-create (efficiently) a slice reference and pass that.
+the function, slice the array to create
+(efficiently) a slice reference and pass that.
+By default, the lower and upper bounds of a slice match the
+ends of the existing object, so the concise notation "[:]"
+will slice the whole array.
Using slices one can write this function (from "sum.go"):
--PROG progs/sum.go /sum/ /^}/
-and invoke it like this:
-
---PROG progs/sum.go /1,2,3/
-
Note how the return type ("int") is defined for "sum()" by stating it
after the parameter list.
-The expression "[3]int{1,2,3}"—a type followed by a
-brace-bounded
-expression—is a constructor for a value, in this case an array
-of 3 "ints".
-Putting an "&"
-in front gives us the address of a unique instance of the value. We pass the
-pointer to "sum()" by (implicitly) promoting it to a slice.
+
+To call the function, we slice the array. This intricate call (we'll show
+a simpler way in a moment) constructs
+an array and slices it:
+
+ s := sum([3]int{1,2,3}[:])
If you are creating a regular array but want the compiler to count the
elements for you, use "..." as the array size:
- s := sum(&[...]int{1,2,3})
+ s := sum([...]int{1,2,3}[:])
-In practice, though, unless you're meticulous about storage layout within a
-data structure, a slice itself—using empty brackets and no
-"&"—is all you need:
+That's fussier than necessary, though.
+In practice, unless you're meticulous about storage layout within a
+data structure, a slice itself—using empty brackets with no size—is all you need:
s := sum([]int{1,2,3})
diff --git a/doc/progs/cat.go b/doc/progs/cat.go
index f8d1a54fb8..697e5f7865 100644
--- a/doc/progs/cat.go
+++ b/doc/progs/cat.go
@@ -15,11 +15,11 @@ func cat(f *file.File) {
const NBUF = 512
var buf [NBUF]byte
for {
- switch nr, er := f.Read(&buf); true {
+ switch nr, er := f.Read(buf[:]); true {
case nr < 0:
fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", f.String(), er.String())
os.Exit(1)
- case nr == 0: // EOF
+ case nr == 0: // EOF
return
case nr > 0:
if nw, ew := file.Stdout.Write(buf[0:nr]); nw != nr {
@@ -30,7 +30,7 @@ func cat(f *file.File) {
}
func main() {
- flag.Parse() // Scans the arg list and sets up flags
+ flag.Parse() // Scans the arg list and sets up flags
if flag.NArg() == 0 {
cat(file.Stdin)
}
diff --git a/doc/progs/cat_rot13.go b/doc/progs/cat_rot13.go
index 42c6195fb9..03fc02259a 100644
--- a/doc/progs/cat_rot13.go
+++ b/doc/progs/cat_rot13.go
@@ -15,10 +15,10 @@ var rot13Flag = flag.Bool("rot13", false, "rot13 the input")
func rot13(b byte) byte {
if 'a' <= b && b <= 'z' {
- b = 'a' + ((b - 'a') + 13) % 26
+ b = 'a' + ((b-'a')+13)%26
}
if 'A' <= b && b <= 'Z' {
- b = 'A' + ((b - 'A') + 13) % 26
+ b = 'A' + ((b-'A')+13)%26
}
return b
}
@@ -29,7 +29,7 @@ type reader interface {
}
type rotate13 struct {
- source reader
+ source reader
}
func newRotate13(source reader) *rotate13 {
@@ -57,11 +57,11 @@ func cat(r reader) {
r = newRotate13(r)
}
for {
- switch nr, er := r.Read(&buf); {
+ switch nr, er := r.Read(buf[:]); {
case nr < 0:
fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", r.String(), er.String())
os.Exit(1)
- case nr == 0: // EOF
+ case nr == 0: // EOF
return
case nr > 0:
nw, ew := file.Stdout.Write(buf[0:nr])
@@ -73,7 +73,7 @@ func cat(r reader) {
}
func main() {
- flag.Parse() // Scans the arg list and sets up flags
+ flag.Parse() // Scans the arg list and sets up flags
if flag.NArg() == 0 {
cat(file.Stdin)
}
diff --git a/doc/progs/sum.go b/doc/progs/sum.go
index 74fd5bca3a..9caa799fdd 100644
--- a/doc/progs/sum.go
+++ b/doc/progs/sum.go
@@ -6,7 +6,7 @@ package main
import "fmt"
-func sum(a []int) int { // returns an int
+func sum(a []int) int { // returns an int
s := 0
for i := 0; i < len(a); i++ {
s += a[i]
@@ -16,6 +16,6 @@ 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
+ s := sum([3]int{1, 2, 3}[:]) // a slice of the array is passed to sum
fmt.Print(s, "\n")
}