add go1.20-examples

Author: bigwhite

go1.20-examples/lang/comparable.go

@@ -0,0 +1,10 @@
+package main
+
+func doSth[T comparable](t T) {
+}
+
+func main() {
+	n := 2
+	var i interface{} = n
+	doSth(i)
+}

go1.20-examples/lang/comparable1.go

@@ -0,0 +1,17 @@
+package main
+
+func doSth[T comparable](t1, t2 T) {
+	if t1 != t2 {
+		println("unequal")
+		return
+	}
+	println("equal")
+}
+
+func main() {
+	n1 := []byte{2}
+	n2 := []byte{3}
+	var i interface{} = n1
+	var j interface{} = n2
+	doSth(i, j)
+}

go1.20-examples/lang/slice2arr.go

@@ -0,0 +1,27 @@
+package main
+
+import "fmt"
+
+func slice2arrOK() {
+	var sl = []int{1, 2, 3, 4, 5, 6, 7}
+	var arr = [7]int(sl)
+	var parr = (*[7]int)(sl)
+	fmt.Println(sl)  // [1 2 3 4 5 6 7]
+	fmt.Println(arr) // [1 2 3 4 5 6 7]
+	sl[0] = 11
+	fmt.Println(arr)  // [1 2 3 4 5 6 7]
+	fmt.Println(parr) // &[11 2 3 4 5 6 7]
+}
+
+func slice2arrPanic() {
+	var sl = []int{1, 2, 3, 4, 5, 6, 7}
+	fmt.Println(sl)
+	var arr = [8]int(sl) // panic: runtime error: cannot convert slice with length 7 to array or pointer to array with length 8
+	fmt.Println(arr)     // &[11 2 3 4 5 6 7]
+
+}
+
+func main() {
+	slice2arrOK()
+	slice2arrPanic()
+}

go1.20-examples/lang/unsafe.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"fmt"
+	"unsafe"
+)
+
+func main() {
+	var arr = [6]byte{'h', 'e', 'l', 'l', 'o', '!'}
+	s := unsafe.String(&arr[0], 6)
+	fmt.Println(s) // hello!
+	arr[0] = 'j'
+	fmt.Println(s) // jello!
+
+	s1 := "golang"
+	fmt.Println(s1) // golang
+	b := unsafe.StringData(s1)
+	*b = 'h' // fatal error: fault, unexpected fault address 0x10a67e5
+	fmt.Println(s1)
+}

go1.20-examples/library/context.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"context"
+	"fmt"
+)
+
+func main() {
+	myError := fmt.Errorf("%s", "myError")
+	ctx, cancel := context.WithCancelCause(context.Background())
+	cancel(myError)
+	fmt.Println(ctx.Err())          // returns context.Canceled
+	fmt.Println(context.Cause(ctx)) // returns myError
+}

go1.20-examples/tools/compiler/local_type_decl.go

@@ -0,0 +1,10 @@
+package main
+
+func F[T1 any]() {
+	type x struct{}
+	type y = x
+}
+
+func main() {
+	F[int]()
+}