tour of go メモ

Struct Literals

type Vertex struct {
    X, Y int
}

var (
    v1 = Vertex{1, 2}  // has type Vertex
    v2 = Vertex{X: 1}  // Y:0 is implicit
    v3 = Vertex{}      // X:0 and Y:0
    p  = &Vertex{1, 2} // has type *Vertex
)

func main() {
    fmt.Println(v1, p, v2, v3)
}

v1 = Vertex{1, 2} と　p = &Vertex{1, 2} の違い｡

If you say
p := Vertex{1,2}

Then you create a new Vertex structure and assign it to the variable p. p has type Vertex.

If you do
q := &Vertex{1,2}

create a new Vertex structure, take a reference to it, and assign that reference to q.
q has type *Vertex.

Just like having a Vertex and a pointer to a vertex are different, so is doing Vertex{1,2} and &Vertex{1,2}

go-lang nuts より

Array,Map関係

array

Go's arrays are values....This means that when you assign or pass around an array value you will make a copy of its contents...

One way to think about arrays is as a sort of struct but with indexed rather than named fields: a fixed-size composite value.
b := [2]string{"Penn", "Teller"}

var [4]int -> [int] [int] [int] [int]
http://blog.golang.org/

slice

Arrays..are a bit inflexible,..Slices, though, are everywhere. They build on arrays to provide great power and convenience.

letters := []string{"a", "b", "c", "d"}

A slice can be created with ...make. The make function takes a type, a length, and an optional capacity.
len -> length
cap -> capacity

var s []byte
s = make([]byte, 5, 5)
// s == []byte{0, 0, 0, 0, 0}

Capacity and Length

Cap -> length of underlying array.
Len -> length of array.

func main() {
    elements := []int{100, 200, 300}

    // Capacity is now 3.
    fmt.Println(cap(elements))

    // Append another element to the slice.
    elements = append(elements, 400)

    // Capacity is now 6—it has doubled.
    fmt.Println(cap(elements))

    // Create an empty slice.
    // ... Its length is 0.
    items := []string{}
    fmt.Println(len(items))

    // Append a string and the slice now has a length of 1.
    items = append(items, "cat")
    fmt.Println(len(items))

}
http://www.dotnetperls.com/

append

test_array - []string{}

GO: append(test_array, "x", "y", "z")
-> Ruby: test_array << ["x", "y", "z"]

range and iteration

The range keyword is used with a for-loop. When we use range on a slice, all the indexes in the slice are enumerated.

var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}

func main() {
    for index, value := range pow {
        fmt.Println(index, value)
    }
    for _, value := range pow {
        fmt.Println(value)
    }
    for index, _ := range pow {
        fmt.Println(index)
          fmt.Println(index, _) // -> !!エラー!!
    }
}