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example.go
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example.go
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package main
import (
"fmt"
)
type vertex struct {
x, y int
}
func main() {
fmt.Printf("Variables Example results = %d\n", variables())
pointers()
slices()
maps()
}
func variables() (variableResult int) {
//Explicit type declartion
var var1, var2, var3 int = 1, 2, 3
//The type is implied
var4, var5, var6 := 4, 5, 6
//variableResult is a named result parameter
variableResult = var1 + var2 + var3 + var4 + var5 + var6
//Don't need to return anything since variableResult was assigned above.
return
}
func pointers() {
vertexOrignal := vertex{1, 2}
//This is going to make a copy of the orginal.
vertexCopy := vertexOrignal
vertexCopy.x = 3
vertexCopy.y = 4
fmt.Println("Pointer Example")
fmt.Printf("Copy variable changed Original x = %d y = %d\n", vertexOrignal.x, vertexOrignal.y)
//This will give you a reference to the pointer
vertexReference := &vertexOrignal
vertexReference.x = 3
vertexReference.y = 4
fmt.Printf("Pointer variable changed Original x = %d y = %d\n", vertexOrignal.x, vertexOrignal.y)
//Create a pointer
vertexPointer := &vertex{5, 6}
vertexPointerRef := vertexPointer
vertexPointerRef.x++
vertexPointerRef.y++
//This will give you the value at the pointer
vertexValue := *vertexPointer
fmt.Printf("Vertex Pointer change x = %d y = %d\n", vertexValue.x, vertexValue.y)
return
}
func slices() {
sliceLength()
sliceNil()
mutatingSlices()
}
func sliceLength() {
//Create array with length of five
sliceWithLength := make([]vertex, 5)
for i := 0; i < len(sliceWithLength); i++ {
sliceWithLength[i] = vertex{i, i + 1}
}
fmt.Println("Slice Example")
fmt.Printf("Slice with length = %v\n", sliceWithLength)
}
func sliceNil() {
//Create a nil slice.
var sliceWithNil []vertex
for i := 0; i < 5; i++ {
//Must append to array since the slice is nil.
//This will be costly to performance.
sliceWithNil = append(sliceWithNil, vertex{i, i + 1})
}
fmt.Printf("Slice nil = %v\n", sliceWithNil)
}
func mutatingSlices() {
sliceVertices := make([]vertex, 5)
for i := 0; i < len(sliceVertices); i++ {
sliceVertices[i] = vertex{i, i + 1}
}
//Changing values won't change the slice
changeValues(sliceVertices)
fmt.Printf("After change values = %v\n", sliceVertices)
//Change the references will change the slice
changeReferences(sliceVertices)
fmt.Printf("After change references = %v\n", sliceVertices)
//Make a slice of pointers so you always have a reference
slicePointers := make([]*vertex, 5)
for i := 0; i < len(slicePointers); i++ {
slicePointers[i] = &vertex{i, i + 1}
}
//Change the array of pointers.
changePointers(slicePointers)
//Create an array of values
sliceValues := make([]vertex, 5)
for i := 0; i < len(slicePointers); i++ {
//Gets the value
sliceValues[i] = *slicePointers[i]
}
fmt.Printf("After slice of pointers change = %v\n", sliceValues)
}
func changeValues(vertices []vertex) {
for _, vertex := range vertices {
vertex.x++
vertex.y++
}
return
}
func changeReferences(vertices []vertex) {
for i := 0; i < len(vertices); i++ {
vertex := &vertices[i]
vertex.x++
vertex.y++
}
return
}
func changePointers(vertices []*vertex) {
for _, vertex := range vertices {
vertex.x++
vertex.y++
}
return
}
func maps() {
mapValues := make(map[int]vertex)
for i := 0; i < 5; i++ {
mapValues[i] = vertex{i, i + 1}
}
fmt.Printf("Original Map = %v\n", mapValues)
mutatingMaps()
}
func mutatingMaps() {
mapPointers := make(map[int]*vertex)
for i := 0; i < 5; i++ {
mapPointers[i] = &vertex{i, i + 1}
}
for i := 0; i < 5; i++ {
mapPointers[i].x++
mapPointers[i].y++
}
//Get the values from the map of pointers.
mapValues := make(map[int]vertex)
for i := 0; i < 5; i++ {
mapValues[i] = *mapPointers[i]
}
fmt.Printf("Mutated Map = %v\n", mapValues)
}