Differences

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--- go_tour_notes [2018/04/13 09:13] – [Methods and type aliasing] rpjday
+++ go_tour_notes [2018/04/14 08:57] (current) – [Refresher: pointer-based function] rpjday
@@ Line 623: / Line 623: @@
 ===== Methods =====
-==== Non-method Abs() ====
+==== Non-method Abs() function ====
 Non-method ''Abs()'' function for ''Vertex'', which takes a ''Vertex'' as a regular argument (no polymorphism)
@@ Line 651: / Line 651: @@
 }
-func (v Vertex) Abs() float64 {
+func (v Vertex) Abs() float64 {        // receiver argument
 	return math.Sqrt(v.X*v.X + v.Y*v.Y)
 }
@@ Line 662: / Line 662: @@
 </code>
-==== Methods and type aliasing ====
+==== Methods and type "aliasing" ====
 You can declare a method on non-struct types, too. Below, we see a numeric type ''MyFloat'' with an ''Abs'' method:
@@ Line 684: / Line 684: @@
 You can only declare a method with a receiver whose type is defined in the same package as the method. You //cannot// declare a method with a receiver whose type is defined in another package (which includes the built-in types such as ''int'').
-==== Pointer receivers ====
+===== Methods with pointer receivers =====
+==== Refresher: call-by-value ====
+Call-by-value function, which makes a //copy// of the argument:
 <code>
+package main
+import (
+        "fmt"
+)
 type Vertex struct {
-	X, Y float64
+        X, Y float64
 }
-func (v Vertex) Abs() float64 {
+func Scale(v Vertex, f float64) Vertex {
-	return math.Sqrt(v.X*v.X + v.Y*v.Y)
+        v.X = v.X * f
+        v.Y = v.Y * f
+        return v
 }
-func (v *Vertex) Scale(f float64) {
+func main() {
-	v.X = v.X * f
+        v := Vertex{3, 4}
-	v.Y = v.Y * f
+        fmt.Println(v)
+        fmt.Println(Scale(v, 10))
+        fmt.Println(v)
 }
+{3 4}
+{30 40}
+{3 4}
 </code>
+==== Refresher: pointer-based function ====
+Pointer-based call:
+<code>
+package main
+import (
+        "fmt"
+)
+type Vertex struct {
+        X, Y float64
+}
+func Scale(v *Vertex, f float64) {
+        v.X = v.X * f
+        v.Y = v.Y * f
+}
+func main() {
+        v := Vertex{3, 4}
+        fmt.Println(v)
+        Scale(&v, 10)
+        fmt.Println(v)
+}
+{3 4}
+{30 40}
+</code>
+Notes about the above:
+  * Even if the arg is a pointer, Go allows you to use "." to dereference.
+  * You cannot support both variations of that function