2022年1月12日

function/fib2.go

+package main
+
+import (
+	"fmt"
+	"io"
+	"strings"
+)
+
+// 1, 1, 2, 3, 5, 8, 13, 21, 34, ...
+func Fibonaccis() func() int {
+	a, b := 0, 1
+	return func() int {
+		a, b = b, a+b
+		return a
+	}
+}
+
+type intGens struct {
+	gen           func() int
+	currentReader io.Reader
+}
+
+func (g *intGens) Read(
+	p []byte) (n int, err error) {
+	err = io.EOF
+	if g.currentReader != nil {
+		n, err = g.currentReader.Read(p)
+	}
+	if err == io.EOF {
+		next := g.gen()
+		s := fmt.Sprintf("%d\n", next)
+		g.currentReader = strings.NewReader(s)
+		if n == 0 {
+			n, err = g.currentReader.Read(p)
+		}
+	}
+	return n, err
+}
+
+func main() {
+	f := &intGens{
+		gen: Fibonaccis(),
+	}
+	for i := 0; i < 20; i++ {
+		b := make([]byte, 1)
+		n, err := f.Read(b)
+		fmt.Printf("%d bytes read: %q. err = %v \n", n, b, err)
+	}
+}