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improving chapter 2.6

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ldynia
2017-07-16 19:32:51 +02:00
parent 367ff44de6
commit 8b460337bf
1 changed files with 70 additions and 63 deletions
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133
en/02.6.md
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@@ -20,7 +20,6 @@ This combination of methods is called an interface and is implemented by both St
An interface defines a set of methods, so if a type implements all the methods we say that it implements the interface.
```Go
type Human struct {
name string
age int
@@ -39,33 +38,7 @@ type Employee struct {
money float32
}
func (h *Human) SayHi() {
fmt.Printf("Hi, I am %s you can call me on %s\n", h.name, h.phone)
}
func (h *Human) Sing(lyrics string) {
fmt.Println("La la, la la la, la la la la la...", lyrics)
}
func (h *Human) Guzzle(beerStein string) {
fmt.Println("Guzzle Guzzle Guzzle...", beerStein)
}
// Employee overloads Sayhi
func (e *Employee) SayHi() {
fmt.Printf("Hi, I am %s, I work at %s. Call me on %s\n", e.name,
e.company, e.phone) //Yes you can split into 2 lines here.
}
func (s *Student) BorrowMoney(amount float32) {
s.loan += amount // (again and again and...)
}
func (e *Employee) SpendSalary(amount float32) {
e.money -= amount // More vodka please!!! Get me through the day!
}
// define interface
// define interfaces
type Men interface {
SayHi()
Sing(lyrics string)
@@ -84,6 +57,31 @@ type ElderlyGent interface {
SpendSalary(amount float32)
}
func (h *Human) SayHi() {
fmt.Printf("Hi, I am %s you can call me on %s\n", h.name, h.phone)
}
func (h *Human) Sing(lyrics string) {
fmt.Println("La la, la la la, la la la la la...", lyrics)
}
func (h *Human) Guzzle(beerStein string) {
fmt.Println("Guzzle Guzzle Guzzle...", beerStein)
}
// Employee overloads SayHi
func (e *Employee) SayHi() {
fmt.Printf("Hi, I am %s, I work at %s. Call me on %s\n", e.name,
e.company, e.phone) //Yes you can split into 2 lines here.
}
func (s *Student) BorrowMoney(amount float32) {
s.loan += amount // (again and again and...)
}
func (e *Employee) SpendSalary(amount float32) {
e.money -= amount // More vodka please!!! Get me through the day!
}
```
We know that an interface can be implemented by any type, and one type can implement many interfaces simultaneously.
@@ -117,25 +115,28 @@ type Employee struct {
money float32
}
func (h Human) SayHi() {
fmt.Printf("Hi, I am %s you can call me on %s\n", h.name, h.phone)
}
func (h Human) Sing(lyrics string) {
fmt.Println("La la la la...", lyrics)
}
func (e Employee) SayHi() {
fmt.Printf("Hi, I am %s, I work at %s. Call me on %s\n", e.name,
e.company, e.phone) //Yes you can split into 2 lines here.
}
// Interface Men implemented by Human, Student and Employee
type Men interface {
SayHi()
Sing(lyrics string)
}
// method
func (h Human) SayHi() {
fmt.Printf("Hi, I am %s you can call me on %s\n", h.name, h.phone)
}
// method
func (h Human) Sing(lyrics string) {
fmt.Println("La la la la...", lyrics)
}
// method
func (e Employee) SayHi() {
fmt.Printf("Hi, I am %s, I work at %s. Call me on %s\n", e.name,
e.company, e.phone) //Yes you can split into 2 lines here.
}
func main() {
mike := Student{Human{"Mike", 25, "222-222-XXX"}, "MIT", 0.00}
paul := Student{Human{"Paul", 26, "111-222-XXX"}, "Harvard", 100}
@@ -167,8 +168,7 @@ func main() {
value.SayHi()
}
}
```
```
An interface is a set of abstract methods, and can be implemented by non-interface types. It cannot therefore implement itself.
### Empty interface
@@ -176,25 +176,29 @@ An interface is a set of abstract methods, and can be implemented by non-interfa
An empty interface is an interface that doesn't contain any methods, so all types implement an empty interface. This fact is very useful when we want to store all types at some point, and is similar to void* in C.
```Go
// define a as empty interface
var a interface{}
var i int = 5
var void interface{}
// vars
i := 5
s := "Hello world"
// a can store value of any type
a = i
a = s
void = i
void = s
```
If a function uses an empty interface as its argument type, it can accept any type; if a function uses empty interface as its return value type, it can return any type.
### Method arguments of an interface
Any variable can be used in an interface. So how can we use this feature to pass any type of variable to a function?
For example we use fmt.Println a lot, but have you ever noticed that it can accept any type of argument? Looking at the open source code of fmt, we see the following definition.
For example we use `fmt.Println` a lot, but have you ever noticed that it can accept any type of argument? Looking at the open source code of `fmt`, we see the following definition.
```Go
type Stringer interface {
String() string
}
```
```
This means any type that implements interface Stringer can be passed to fmt.Println as an argument. Let's prove it.
```Go
package main
@@ -210,7 +214,7 @@ type Human struct {
phone string
}
// Human implemented fmt.Stringer
// Human implements fmt.Stringer
func (h Human) String() string {
return "Name:" + h.name + ", Age:" + strconv.Itoa(h.age) + " years, Contact:" + h.phone
}
@@ -219,18 +223,18 @@ func main() {
Bob := Human{"Bob", 39, "000-7777-XXX"}
fmt.Println("This Human is : ", Bob)
}
```
```
Looking back to the example of Box, you will find that Color implements interface Stringer as well, so we are able to customize the print format. If we don't implement this interface, fmt.Println prints the type with its default format.
```Go
fmt.Println("The biggest one is", boxes.BiggestsColor().String())
fmt.Println("The biggest one is", boxes.BiggestsColor())
```
```
Attention: If the type implemented the interface `error`, fmt will call `Error()`, so you don't have to implement Stringer at this point.
### Type of variable in an interface
If a variable is the type that implements an interface, we know that any other type that implements the same interface can be assigned to this variable. The question is how can we know the specific type stored in the interface. There are two ways which I will show you.
If a variable is the type that implements an interface, we know that any other type that implements the same interface can be assigned to this variable. The question is how can we know the specific type stored in the interface. There are two ways which I will show you.
- Assertion of Comma-ok pattern
@@ -284,7 +288,7 @@ It's quite easy to use this pattern, but if we have many types to test, we'd bet
- switch test
Let's use `switch` to rewrite the above example.
```Go
```Go
package main
import (
@@ -325,7 +329,7 @@ func main() {
}
```
One thing you should remember is that `element.(type)` cannot be used outside of the `switch` body, which means in that case you have to use the `comma-ok` pattern .
### Embedded interfaces
@@ -351,7 +355,7 @@ type Interface interface {
// Swap swaps the elements with indexes i and j.
Swap(i, j int)
}
```
```
Another example is the `io.ReadWriter` in package `io`.
```Go
// io.ReadWriter
@@ -359,30 +363,33 @@ type ReadWriter interface {
Reader
Writer
}
```
```
### Reflection
Reflection in Go is used for determining information at runtime. We use the `reflect` package, and this official [article](http://golang.org/doc/articles/laws_of_reflection.html) explains how reflect works in Go.
Reflection in Go is used for determining information at runtime. We use the `reflect` package, and [The Laws of Reflection](http://golang.org/doc/articles/laws_of_reflection.html) post explains how reflect works in Go.
There are three steps involved when using reflect. First, we need to convert an interface to reflect types (reflect.Type or reflect.Value, this depends on the situation).
```Go
t := reflect.TypeOf(i) // get meta-data in type i, and use t to get all elements
v := reflect.ValueOf(i) // get actual value in type i, and use v to change its value
```
```
After that, we can convert the reflected types to get the values that we need.
```Go
var x float64 = 3.4
t := reflect.TypeOf(x)
v := reflect.ValueOf(x)
fmt.Println("type:", v.Type())
fmt.Println("type:", t)
fmt.Println("value:", v)
fmt.Println("kind is float64:", v.Kind() == reflect.Float64)
fmt.Println("value:", v.Float())
```
```
Finally, if we want to change the values of the reflected types, we need to make it modifiable. As discussed earlier, there is a difference between pass by value and pass by reference. The following code will not compile.
```Go
var x float64 = 3.4
v := reflect.ValueOf(x)
v.SetFloat(7.1)
```
```
Instead, we must use the following code to change the values from reflect types.
```Go
var x float64 = 3.4