4 Generics

4generics/generic-types.go

@@ -0,0 +1,26 @@
+package main
+
+import "fmt"
+
+// List represents a singly-linked list that holds
+// values of any type.
+type List[T any] struct {
+	next *List[T]
+	val  T
+}
+
+func main() {
+	list := List[any]{}
+	list.next = &List[any]{}
+	list.val = 123
+	list.next.val = "hello"
+
+	fmt.Println(list.val)
+	fmt.Println(list.next.val)
+	fmt.Println(list)
+
+	// NEXT complete linked list implementation
+	// single linked list
+	// doubly linked list
+	// addNode(), addNodeAt(), deleteNode(), deleteNodeAt(), getList() ...
+}

4generics/type-paramaters.go

@@ -0,0 +1,78 @@
+package main
+
+// extra resource: https://go.dev/doc/tutorial/generics
+
+import (
+	"fmt"
+
+	"golang.org/x/exp/constraints"
+)
+
+// interfaces with type elements couldn't be used anywhere other than type paramaters
+type Number interface {
+	int64 | float64
+}
+
+type Myint interface {
+	int64
+}
+
+func SumInt[K comparable, V Myint](m map[K]V) V {
+	var s V
+	for _, v := range m {
+		s += v
+	}
+	return s
+}
+
+func SumIntFloat[K comparable, V Number](m map[K]V) V {
+	var s V
+	for _, v := range m {
+		s += v
+	}
+	return s
+}
+
+func SumAll[K comparable, V constraints.Ordered](m map[K]V) V {
+	var s V
+	for _, v := range m {
+		s += v
+	}
+	return s
+}
+
+func main2() { // change main2 to main befor testing !!!
+	fmt.Println("Go functions can be written to work on multiple types using type parameters")
+	fmt.Println("square bracked types after function names are type paramaters")
+	fmt.Println("You can create type paramaters with keyword `comparable`(for comparable types), `any` for any type or other type name/s.")
+	fmt.Println("See differences between SumInt, SumIntFloat and SumAll")
+	fmt.Println("Please note down map keys should be comparable because of default map behaviour")
+
+	ints := map[string]int64{
+		"first":  1,
+		"second": 2,
+		"third":  3,
+	}
+
+	floats := map[string]float64{
+		"first":  1.23,
+		"second": 2.3123,
+		"third":  3,
+	}
+
+	strings := map[string]string{
+		"first":  "str1",
+		"second": "str2",
+		"third":  "str3",
+	}
+
+	fmt.Println(SumInt(ints))
+	// fmt.Println(SumInt(floats)) // error
+	fmt.Println(SumIntFloat(ints))
+	fmt.Println(SumIntFloat(floats))
+	// fmt.Println(SumIntFloat(strings)) // error
+	fmt.Println(SumAll(ints))
+	fmt.Println(SumAll(floats))
+	fmt.Println(SumAll(strings))
+
+}