publish slices, tweak surrounding

examples/slices/slices.go

@@ -1,14 +1,77 @@
+// _Slices_ are a key data type in Go, giving a more
+// powerful interface to sequences that arrays.
+
 package main
 
 import "fmt"
 
 func main() {
-    slice1 := []int{1, 2, 3}
-    slice2 := append(slice1, 4, 5)
-    fmt.Println(slice1)
-    fmt.Println(slice2)
-    slice3 := make([]int, 2)
-    copy(slice3, slice1)
-    fmt.Println(slice1)
-    fmt.Println(slice3)
+
+    // In contrast to arrays, slices are typed only
+    // by the elements it contains (not the number of
+    // elements). To create an empty slice with non-zero
+    // length, use the builtin `make`. Here we make a
+    // slice of `int`s of length 5.
+    s := make([]int, 5)
+
+    // New slices are initially empty-valued.
+    fmt.Println("emp:", s)
+
+    // We can set and get just like with arrays.
+    s[4] = 100
+    fmt.Println("set:", s)
+    fmt.Println("get:", s[4])
+
+    // `len` returns the length of the slice as expected.
+    fmt.Println("len:", len(s))
+
+    // In addition to these basic operations, slices
+    // support several more that make them richer than
+    // arrays. One is the builtin `append`, which 
+    // returns a slice containing one or more new values.
+    // Note that we need to accapt a return value from
+    // append as we may get a new slice reference.
+    s = append(s, 6)
+    s = append(s, 7, 8)
+    fmt.Println("apd:", s)
+
+    // Slices can also be `copy`'d. Here we create an
+    // empty slice `c` of the same length as `s` and copy
+    // into `c` from `s`.
+    c := make([]int, len(s))
+    copy(c, s)
+    fmt.Println("cpy:", c)
+
+    // Slices support a "slice" operator, which is denoted
+    // with brackets containing a `:`. For example, this
+    // get a slice of the elements 4, 5, and 6.
+    l := s[4:7]
+    fmt.Println("sl1:", l)
+
+    // To slice up the 7th index.
+    l = s[:7]
+    fmt.Println("sl2:", l)
+
+    // Or from the 4th index upwards.
+    l = s[4:]
+    fmt.Println("sl3:", l)
+
+    // We can declare and initalize a slice in a single
+    // line as well.
+    t := []int{1, 2, 3, 4, 5}
+    fmt.Println("dcl:", t)
+
+    // Slices can be composed into multi-dimensional data
+    // structures. The length of the inner slices can
+    // vary, unlike in the case of multi-dimensional
+    // arrays.
+    twoD := make([][]int, 3)
+    for i := 0; i < 3; i++ {
+        innerLen := i + 1
+        twoD[i] = make([]int, innerLen)
+        for j := 0; j < innerLen; j++ {
+            twoD[i][j] = i + j
+        }
+    }
+    fmt.Println("2d: ", twoD)
 }

examples/slices/slices.sh

@@ -0,0 +1,21 @@
+# Note that while slices are different types than arrays,
+# they are rendered similarly by `fmt.Println`.
+$ go run slices.go
+emp: [0 0 0 0 0]
+set: [0 0 0 0 100]
+get: 100
+len: 5
+apd: [0 0 0 0 100 6 7 8]
+cpy: [0 0 0 0 100 6 7 8]
+sl1: [100 6 7]
+sl2: [0 0 0 0 100 6 7]
+sl3: [100 6 7 8]
+dcl: [1 2 3 4 5]
+2d:  [[0] [1 2] [2 3 4]]
+
+# Check out this [great blog post](http://blog.golang.org/2011/01/go-slices-usage-and-internals.html)
+# by the Go team for more details on the design and
+# implementation of slices in Go.
+
+# Now that we've seen arrays and slices we'll look at
+# Go's other key builtin data structure: maps.