Merge pull request #68 from tsingbx/slices

add doc for slices

117-Slices/slices-01.gop

@@ -0,0 +1,18 @@
+# Slice literals in Go+ style
+// A slice is a collection of data elements of the same type. A slice literal is a list of expressions surrounded by square brackets. An individual element can be accessed using an index expression. Indexes start from 0.
+//
+// In go+, you can get slice length directly from len method, and you can casting slice literals:
+
+f64 := []float64([1, 2, 3]) // []float64
+println(f64, f64.len)       // get length by len method
+
+nums := [1, 2, 3]
+println nums      // [1 2 3]
+println nums.len  // 3, go+ support
+println nums[0]   // 1
+println nums[1:3] // [2 3]
+println nums[:2]  // [1 2]
+println nums[2:]  // [3]
+
+nums[1] = 5
+println nums // [1 5 3]

117-Slices/slices-02.gop

@@ -0,0 +1,6 @@
+# Slice
+// An array has a fixed size. A slice, on the other hand, is a dynamically-sized, flexible view into the elements of an array. In practice, slices are much more common than arrays.
+//
+// The type []T is a slice with elements of type T.
+//
+// A slice is formed by specifying two indices, a low and high bound, separated by a colon: a[low : high]. This selects a half-open range which includes the first element, but excludes the last one.

117-Slices/slices-03.gop

@@ -0,0 +1,22 @@
+# Slices are like references to arrays
+// A slice does not store any data, it just describes a section of an underlying array.
+//
+// Changing the elements of a slice modifies the corresponding elements of its underlying array.
+//
+// Other slices that share the same underlying array will see those changes.
+
+names := [4]string{
+	"John",
+	"Paul",
+	"George",
+	"Ringo",
+}
+println names
+
+a := names[0:2]
+b := names[1:3]
+println a, b
+
+b[0] = "XXX"
+println a, b
+println names

117-Slices/slices-04.gop

@@ -0,0 +1,27 @@
+# Slice literals
+// A slice literal is like an array literal without the length.
+// <pre>
+// This is an array literal:
+// [3]bool{true, true, false}
+// And this creates the same array as above, then builds a slice that references it:
+// []bool{true, true, false}
+// </pre>
+
+q := []int{2, 3, 5, 7, 11, 13}
+println q
+
+r := []bool{true, false, true, true, false, true}
+println r
+
+s := []struct {
+	i int
+	b bool
+}{
+	{2, true},
+	{3, false},
+	{5, true},
+	{7, true},
+	{11, false},
+	{13, true},
+}
+println s

117-Slices/slices-05.gop

@@ -0,0 +1,23 @@
+# Slice defaults
+// When slicing, you may omit the high or low bounds to use their defaults instead.
+//
+// The default is zero for the low bound and the length of the slice for the high bound.
+//<pre>
+// For the array
+// var a [10]int
+// these slice expressions are equivalent:
+// a[0:10]
+// a[:10]
+// a[0:]
+// a[:]
+//</pre>
+s := []int{2, 3, 5, 7, 11, 13}
+
+s = s[1:]
+println s
+
+s = s[1:4]
+println s
+
+s = s[:2]
+println s

117-Slices/slices-06.gop

@@ -0,0 +1,26 @@
+# Slice length and capacity
+// A slice has both a length and a capacity.
+//
+// The length of a slice is the number of elements it contains.
+//
+// The capacity of a slice is the number of elements in the underlying array, counting from the first element in the slice.
+//
+// The length and capacity of a slice s can be obtained using the expressions len(s) and cap(s).
+//
+// You can extend a slice's length by re-slicing it, provided it has sufficient capacity. Try changing one of the slice operations in the example program to extend it beyond its capacity and see what happens.
+
+func printSlice(s []int) {
+	printf "len=%d cap=%d %v\n", len(s), cap(s), s
+}
+
+s := []int{2, 3, 5, 7, 11, 13}
+printSlice s
+
+s = s[:0] // Slice the slice to give it zero length.
+printSlice s
+
+s = s[:4] // Extend its length.
+printSlice s
+
+s = s[2:] // Drop its first two values.
+printSlice s

117-Slices/slices-07.gop

@@ -0,0 +1,12 @@
+# Nil slices
+// The zero value of a slice is nil.
+//
+// A nil slice has a length and capacity of 0 and has no underlying array.
+
+var s []int
+
+println s, len(s), cap(s)
+
+if s == nil {
+	println "nil!"
+}

117-Slices/slices-08.gop

@@ -0,0 +1,29 @@
+# Creating a slice with make
+// Slices can be created with the built-in make function; this is how you create dynamically-sized arrays.
+//
+// The make function allocates a zeroed array and returns a slice that refers to that array:
+//
+//<pre>
+//a := make([]int, 5)			// len(a)=5
+//To specify a capacity, pass a third argument to make:
+//b := make([]int, 0, 5) 		// len(b)=0, cap(b)=5
+//b = b[:cap(b)] 				// len(b)=5, cap(b)=5
+//b = b[1:]      				// len(b)=4, cap(b)=4
+//</pre>
+
+func printSlice(s string, x []int) {
+	printf "%s len=%d cap=%d %v\n",
+		s, len(x), cap(x), x
+}
+
+a := make([]int, 5)
+printSlice "a", a
+
+b := make([]int, 0, 5)
+printSlice "b", b
+
+c := b[:2]
+printSlice "c", c
+
+d := c[2:5]
+printSlice "d", d

117-Slices/slices-09.gop

@@ -0,0 +1,23 @@
+# Slices of slices
+// Slices can contain any type, including other slices.
+// Create a tic-tac-toe board.
+
+import (
+	"strings"
+)
+
+board := [][]string{
+	[]string{"_", "_", "_"},
+	[]string{"_", "_", "_"},
+	[]string{"_", "_", "_"},
+}
+
+board[0][0] = "X" // The players take turns.
+board[2][2] = "O"
+board[1][2] = "X"
+board[1][0] = "O"
+board[0][2] = "X"
+
+for i := 0; i < len(board); i++ {
+	printf "%s\n", strings.join(board[i], " ")
+}

117-Slices/slices-10.gop

@@ -0,0 +1,27 @@
+# Appending to a slice
+// It is common to append new elements to a slice, and so Go provides a built-in append function. The documentation of the built-in package describes append.
+//
+// func append(s []T, vs ...T) []T
+//
+// The first parameter s of append is a slice of type T, and the rest are T values to append to the slice.
+//
+// The resulting value of append is a slice containing all the elements of the original slice plus the provided values.
+//
+// If the backing array of s is too small to fit all the given values a bigger array will be allocated. The returned slice will point to the newly allocated array.
+
+func printSlice(s []int) {
+	printf "len = %d cap = %d %v\n", len(s), cap(s), s
+}
+
+var s []int
+
+printSlice s
+
+s = append(s, 0) // append works on nil slices.
+printSlice s
+
+s = append(s, 1) // The slice grows as needed.
+printSlice s
+
+s = append(s, 2, 3, 4) // We can add more than one element at a time.
+printSlice s

117-Slices/slices-11.gop

@@ -0,0 +1,10 @@
+# Range
+// The range form of the for loop iterates over a slice or map.
+//
+// When ranging over a slice, two values are returned for each iteration. The first is the index, and the second is a copy of the element at that index.
+
+var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}
+
+for i, v := range pow {
+	printf "2**%d = %d\n", i, v
+}

117-Slices/slices-12.gop

@@ -0,0 +1,17 @@
+# Range continued
+//
+// <pre>
+// You can skip the index or value by assigning to _.
+// for i, _ := range pow
+// for _, value := range pow
+// If you only want the index, you can omit the second variable.
+// for i := range pow
+// </pre>
+
+pow := make([]int, 10)
+for i := range pow {
+	pow[i] = 1 << uint(i) // == 2**i
+}
+for _, value := range pow {
+	printf "%d\n", value
+}