Joe Wood Notes

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Variables

func main() {
    var x int = 100
    fmt.Println(x)
}

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Constants

Go has true constants defined using const:

const PI float64 = 3.1415

func main() {
    const count int = 10 // Constants cannot be modified
    var mutableCount int = 10
    mutableCount += 1 // Allowed
    fmt.Println(PI, mutableCount)
}

• Variables must have an explicit type or use := for type inference.

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Literals

Go supports various literals:

func main() {
    var myInt int = 10
    var myBinary int = 0b1010
    var myOctal int = 0o12
    var myHex int = 0xA
    var myFloat float64 = 10.5
    var mySciNot float64 = 2.0e3
    var myBool bool = true
    var myByte byte = 'A'

    fmt.Println(myInt, myBinary, myOctal, myHex, myFloat, mySciNot, myBool, myByte)
}

For strings, Go supports raw and multi-line strings:

func main() {
    myStr := "hello"
    myStrDouble := "hello"
    myMultiLine := `hello
there`
    myRaw := `New\nLine` // Raw string, ignores escape sequences
    name := "Go"
    myFormatted := fmt.Sprintf("Hello %s", name)

    fmt.Println(myStr, myStrDouble, myMultiLine, myRaw, myFormatted)
}

Complex types:

func main() {
    myArray := [3]int{1, 2, 3, 4, 5, 6}          // [3]int (array with fixed length)
    slice := arr[1:4]              // Slice referencing elements {2, 3, 4}
    emptySlice := []int{}  // Empty slice
    addSlice = append(slice, 100)
    mySlice := []int{1, 2, 3}           // []int (slice, dynamic array)
    myMap := map[string]int{"age": 30, "score": 100} // map[string]int (dictionary)
    mySet := map[int]struct{}{1: {}, 2: {}, 3: {}} // map[int]struct{} (set workaround)
    myBytes := []byte("hello")          // []byte (byte slice)
    fmt.Printf("After append %d: len=%d cap=%d %v\n", i, len(slice), cap(slice), slice)

    copySlice := make([]int, len(original)) // Allocate new memory
    copy(copySlice, original)               // Copy values

}

You can create an immutable slice to prevent unexpected mutations on the underlying array by using a wrapper (this is a workaround)

// Read-only slice wrapper
type ReadOnlySlice interface {
    Get(index int) int
    Length() int
}

// ImmutableSlice struct
type ImmutableSlice struct {
    data []int
}

// Methods to enforce read-only access
func (s ImmutableSlice) Get(index int) int {
    return s.data[index]
}

func (s ImmutableSlice) Length() int {
    return len(s.data)
}

func main() {
    original := []int{1, 2, 3, 4, 5}
    readOnly := ImmutableSlice{data: original}

    fmt.Println("Element at index 2:", readOnly.Get(2)) //  Allowed
    // readOnly.data[2] = 100  // Compilation error if `data` is unexported
}