From 416811ed8b9325e8961536eaf70227d7a2c8f74e Mon Sep 17 00:00:00 2001
From: Fernando Lopes <118869201+plasmus777@users.noreply.github.com>
Date: Tue, 23 Apr 2024 18:29:21 -0300
Subject: [PATCH] Generics

---
 learning/interfaces/interfaces.go |  5 ---
 learning/main.go                  |  7 +++-
 learning/simple/generics.go       | 35 +++++++++++++++++
 learning/simple/interfaces.go     | 65 +++++++++++++++++++++++++++++++
 4 files changed, 105 insertions(+), 7 deletions(-)
 delete mode 100644 learning/interfaces/interfaces.go
 create mode 100644 learning/simple/generics.go
 create mode 100644 learning/simple/interfaces.go

diff --git a/learning/interfaces/interfaces.go b/learning/interfaces/interfaces.go
deleted file mode 100644
index 0ecf0b6..0000000
--- a/learning/interfaces/interfaces.go
+++ /dev/null
@@ -1,5 +0,0 @@
-package interfaces
-
-func Interfaces() {
-
-}
diff --git a/learning/main.go b/learning/main.go
index c1c6654..c40dd6c 100644
--- a/learning/main.go
+++ b/learning/main.go
@@ -6,7 +6,6 @@ import (
 	"github.com/plasmus777/go_lang/learning/arrays"
 	"github.com/plasmus777/go_lang/learning/fluxcontrol"
 	"github.com/plasmus777/go_lang/learning/inheritance"
-	"github.com/plasmus777/go_lang/learning/interfaces"
 	"github.com/plasmus777/go_lang/learning/simple"
 )
 
@@ -36,6 +35,7 @@ func main() {
 		fmt.Println("14 - structs")
 		fmt.Println("15 - inheritance")
 		fmt.Println("16 - interfaces")
+		fmt.Println("17 - generics")
 
 		fmt.Println("")
 		fmt.Println("-1 - exit")
@@ -90,7 +90,10 @@ func main() {
 			inheritance.Inheritance()
 
 		case 16:
-			interfaces.Interfaces()
+			simple.Interfaces()
+
+		case 17:
+			simple.Generics()
 
 		case -1:
 			fmt.Println("Exiting program.")
diff --git a/learning/simple/generics.go b/learning/simple/generics.go
new file mode 100644
index 0000000..848ecab
--- /dev/null
+++ b/learning/simple/generics.go
@@ -0,0 +1,35 @@
+package simple
+
+import "fmt"
+
+func Generics() {
+	slice1 := []int{5, 3, 7, 1}
+	fmt.Println(slice1)
+	fmt.Println(*reverse(slice1))
+
+	fmt.Println()
+
+	slice2 := []string{"b", "g", "a", "m"}
+	fmt.Println(slice2)
+	fmt.Println(*reverse(slice2))
+
+}
+
+//Creating custom constraints can make your code easier to read/understand.
+type customConstraint interface {
+	int | string
+}
+
+//Generics are useful when you want to reuse code dealing with different argument/return types.
+//T is a generic type (in this case, either an int or a string).
+func reverse[T customConstraint](slice []T) *[]T {
+	reverseSlice := make([]T, len(slice))
+
+	j := 0
+	for i := len(slice) - 1; i >= 0; i-- {
+		reverseSlice[j] = slice[i]
+		j++
+	}
+
+	return &reverseSlice
+}
diff --git a/learning/simple/interfaces.go b/learning/simple/interfaces.go
new file mode 100644
index 0000000..c9ceb9d
--- /dev/null
+++ b/learning/simple/interfaces.go
@@ -0,0 +1,65 @@
+package simple
+
+import (
+	"fmt"
+	"math"
+)
+
+// Go does not require the usage of "implements" or similar terms - the implementation is implicit.
+type Geometry interface {
+	Area() float64
+}
+
+func DisplayGeometryArea(g Geometry) {
+	fmt.Println("Area:", g.Area())
+}
+
+type Rectangle struct {
+	height, width float64
+}
+
+type Circle struct {
+	radius float64
+}
+
+func (r *Rectangle) Area() float64 {
+	return r.width * r.height
+}
+
+func (c *Circle) Area() float64 {
+	return math.Pi * math.Pow(c.radius, 2)
+}
+
+func Interfaces() {
+	r := Rectangle{
+		height: 2,
+		width:  4,
+	}
+
+	c := Circle{
+		radius: 3,
+	}
+
+	DisplayGeometryArea(&r)
+	DisplayGeometryArea(&c)
+
+	fmt.Println()
+
+	//The empty interface can have different types of value
+	var slice []interface{}
+
+	slice = append(slice, 10)
+	slice = append(slice, 8.4)
+	slice = append(slice, true)
+	slice = append(slice, "test")
+
+	fmt.Println(slice)
+
+	for index, value := range slice {
+		if val, ok := value.(string); ok {
+			fmt.Println(val+" is a string; index =", index)
+		} else {
+			fmt.Println("index =", index)
+		}
+	}
+}