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// Also available at: https://play.golang.org/p/yTTpB5gB6C |
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package main |
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import ( |
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"fmt" |
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) |
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// ***************************************************************************** |
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// Example 1 - Struct vs Struct with Embedded Type |
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// ***************************************************************************** |
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// Struct types contain fields. You can create instances of struct types. |
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// Struct with 2 fields |
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type Person struct { |
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Name string // field |
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Age int // field |
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} |
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// Struct with 2 fields |
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type Boy1 struct { |
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Person Person // field |
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FavoriteToy string // field |
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} |
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// Struct with 2 fields (1 is an embeded type) |
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type Boy2 struct { |
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Person // anonymous field (embedded type) |
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FavoriteToy string // field |
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} |
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// Struct with 3 fields (1 is an embeded type) |
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// Since Boy3 has an Age field, Person.Age is not longer a promoted field |
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type Boy3 struct { |
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Person // anonymous field (embedded type) |
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FavoriteToy string // field |
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Age int // field (named the same as Person.Age) |
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} |
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func example1() { |
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// Create an instance of the Boy |
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b1 := Boy1{Person{"Jon", 15}, "Corvette"} |
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b2 := Boy2{Person{"Jon", 15}, "Corvette"} |
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b3 := Boy3{Person{"Jon", 15}, "Corvette", 18} |
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// Can ONLY access Age field 1 way |
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fmt.Println(b1.Person.Age) |
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// Output: 15 |
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// Can access Age field 2 ways (b2.Age is called a promoted field) |
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fmt.Println(b2.Person.Age, b2.Age) |
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// Output: 15 15 |
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// Can access Age field 2 ways (b3.Age is NOT a promoted field) |
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fmt.Println(b3.Person.Age, b3.Age) |
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// Output: 15 18 |
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// Can access FavoriteToy field 1 way in both |
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fmt.Println(b1.FavoriteToy) |
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// Output: Corvette |
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fmt.Println(b2.FavoriteToy) |
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// Output: Corvette |
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} |
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// ***************************************************************************** |
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// Example 2 - Named Type Method Sets |
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// ***************************************************************************** |
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// Create named Person type called Man |
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type Man Person |
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// Create named Person type called Woman |
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type Woman Person |
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// Create method increases the age |
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// Can ONLY be used with Man type |
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func (m *Man) IncreaseAge() { |
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m.Age++ |
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} |
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// Create method for only Person that decreases the age |
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// Can ONLY be used with Person type (not with Man or Woman) |
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// *** Can be used with Boy1 or Boy2 |
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func (p *Person) DecreaseAge() { |
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p.Age-- |
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} |
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func example2() { |
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// Create an instance of a Man |
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r := Man{"Steve", 35} |
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// This method can ONLY be called on a Man. It cannot be called on a Woman |
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// or a Person. |
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r.IncreaseAge() |
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// Since Man is NOT a Person, this will throw a compile-time error |
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//r.DecreaseAge() |
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// Print 2 fields |
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fmt.Println(r.Name, r.Age) |
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// Output: Steve 36 |
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} |
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// ***************************************************************************** |
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// Example 3 - Usage of Interfaces |
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// ***************************************************************************** |
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// Interface with a method set |
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type Animal interface { |
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Speak() string |
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} |
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// Named interface is 100% compatible with Animal (not useful though, just good |
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// for aliasing third party interfaces) |
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type LandAnimal Animal |
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// Empty struct |
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type Dog struct { |
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} |
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// Empty struct |
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type Cat struct { |
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} |
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// Create method for the Dog |
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func (d Dog) Speak() string { |
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return "Woof!" |
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} |
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// Receives any type that satisfies the Animal interface |
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func LeaveAtAnimalShelter(a Animal) { |
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fmt.Printf("%T is now at the animal shelter.\n", a) |
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} |
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// This is invalid because a method cannot receive an interface |
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/*func (a Animal) Leave() { |
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fmt.Printf("%T is now at the animal shelter.\n", a) |
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}*/ |
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func example3() { |
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// Create an instance of a Dog |
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d := Dog{} |
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// Call the method |
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fmt.Println(d.Speak()) |
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// Output: Woof! |
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// Call the function and pass the variable |
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LeaveAtAnimalShelter(d) |
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// Output: main.Dog is now at the animal shelter. |
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// ************************************************************************* |
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// This is where it gets interesting |
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// Can also create an instance of either interface by assing in the Dog |
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a := Animal(d) |
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l := LandAnimal(d) |
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// Can even pass in an interface created from an interface that was passed |
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// in the Dog |
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p := LandAnimal(a) |
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// Can call the method |
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fmt.Println(p.Speak()) |
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// Output: Woof! |
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// Can pass any of the instances that are compatible |
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LeaveAtAnimalShelter(a) |
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// Output: main.Dog is now at the animal shelter. |
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LeaveAtAnimalShelter(l) |
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// Output: main.Dog is now at the animal shelter. |
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LeaveAtAnimalShelter(d) |
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// Output: main.Dog is now at the animal shelter. |
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LeaveAtAnimalShelter(p) |
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// Output: main.Dog is now at the animal shelter. |
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/* |
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// Create an instance of a Cat |
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c := Cat{} |
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// This will throw a compile-time error because the Cat does NOT satisfy |
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// the requirements to be an Animal. |
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LeaveAtAnimalShelter(c) |
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// Simple: In order for the Cat to be an Animal, it must have a Speak() |
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// method. |
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// Explanation: In order for the Cat to implement the Animal interface, |
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// it must be associated, at a minimum, with the same method set as the |
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// interface. |
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*/ |
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} |
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// ***************************************************************************** |
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// Main |
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// ***************************************************************************** |
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func main() { |
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example1() |
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example2() |
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example3() |
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} |
josephspurrier revised this gist