good good study, day day up!

vendor/gopl.io/ch6/geometry/geometry.go

@@ -0,0 +1,42 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 156.
+
+// Package geometry defines simple types for plane geometry.
+//!+point
+package geometry
+
+import "math"
+
+type Point struct{ X, Y float64 }
+
+// traditional function
+func Distance(p, q Point) float64 {
+	return math.Hypot(q.X-p.X, q.Y-p.Y)
+}
+
+// same thing, but as a method of the Point type
+func (p Point) Distance(q Point) float64 {
+	return math.Hypot(q.X-p.X, q.Y-p.Y)
+}
+
+//!-point
+
+//!+path
+
+// A Path is a journey connecting the points with straight lines.
+type Path []Point
+
+// Distance returns the distance traveled along the path.
+func (path Path) Distance() float64 {
+	sum := 0.0
+	for i := range path {
+		if i > 0 {
+			sum += path[i-1].Distance(path[i])
+		}
+	}
+	return sum
+}
+
+//!-path