详解Golang中interface接口的原理和使用技巧

    package sort

    // A type, typically a collection, that satisfies sort.Interface can be
    // sorted by the routines in this package.  The methods require that the
    // elements of the collection be enumerated by an integer index.
    type Interface interface {
        // Len is the number of elements in the collection.
        Len() int
        // Less reports whether the element with
        // index i should sort before the element with index j.
        Less(i, j int) bool
        // Swap swaps the elements with indexes i and j.
        Swap(i, j int)
    }
    
    ...
    
    // Sort sorts data.
    // It makes one call to data.Len to determine n, and O(n*log(n)) calls to
    // data.Less and data.Swap. The sort is not guaranteed to be stable.
    func Sort(data Interface) {
        // Switch to heapsort if depth of 2*ceil(lg(n+1)) is reached.
        n := data.Len()
        maxDepth := 0
        for i := n; i > 0; i >>= 1 {
            maxDepth++
        }
        maxDepth *= 2
        quickSort(data, 0, n, maxDepth)
    }

    type Person struct {
    Name string
    Age  int
    }
    
    func (p Person) String() string {
        return fmt.Sprintf("%s: %d", p.Name, p.Age)
    }
    
    // ByAge implements sort.Interface for []Person based on
    // the Age field.
    type ByAge []Person //自定义
    
    func (a ByAge) Len() int           { return len(a) }
    func (a ByAge) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
    func (a ByAge) Less(i, j int) bool { return a[i].Age < a[j].Age }
    
    func main() {
        people := []Person{
            {"Bob", 31},
            {"John", 42},
            {"Michael", 17},
            {"Jenny", 26},
        }
    
        fmt.Println(people)
        sort.Sort(ByAge(people))
        fmt.Println(people)
    }

    func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
        c := newCancelCtx(parent)
        propagateCancel(parent, &c)
        return &c, func() { c.cancel(true, Canceled) }
    }

        // newCancelCtx returns an initialized cancelCtx.
        func newCancelCtx(parent Context) cancelCtx {
            return cancelCtx{
                Context: parent,
                done:    make(chan struct{}),
            }
        }
        
        // A cancelCtx can be canceled. When canceled, it also cancels any children
        // that implement canceler.
        type cancelCtx struct {
            Context     //注意一下这个地方
        
            done chan struct{} // closed by the first cancel call.
            mu       sync.Mutex
            children map[canceler]struct{} // set to nil by the first cancel call
            err      error                 // set to non-nil by the first cancel call
        }
        
        func (c *cancelCtx) Done() <-chan struct{} {
            return c.done
        }
        
        func (c *cancelCtx) Err() error {
            c.mu.Lock()
            defer c.mu.Unlock()
            return c.err
        }
        
        func (c *cancelCtx) String() string {
            return fmt.Sprintf("%v.WithCancel", c.Context)
        }

    func WithCancel(parent Context) (ctx Context, cancel CancelFunc)    //返回 cancelCtx
    func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc) //返回 timerCtx
    func WithValue(parent Context, key, val interface{}) Context    //返回 valueCtx

    // 定义一个 SimpleLog 接口
    type SimpleLog interface {
        Print()
    }
    
    func TestFunc(x SimpleLog) {}
   
    // 定义一个 PrintImpl 结构，用来实现 SimpleLog 接口
    type PrintImpl struct {}
    // PrintImpl 对象实现了SimpleLog 接口的所有方法(本例中是 Print 方法)，就说明实现了  SimpleLog 接口
    func (p *PrintImpl) Print() {
    
    }
    
    func main() {
        var p PrintImpl
        TestFunc(p)
    }

var v1 interface{} = 1
var v2 interface{} = "abc"
var v3 interface{} = struct{ X int }{1}

	Persist(context context.Context, msg interface{}) bool

type Integer int
func (a Integer) Less(b Integer) bool {
    return a < b
}
func (a *Integer) Add(b Integer) {
    *a += b
}
type LessAdder interface { 
    Less(b Integer) bool 
    Add(b Integer)
}
var a Integer = 1
var b1 LessAdder = &a  //OK
var b2 LessAdder = a   //not OK

        var r io.Reader = new(os.File)
        var rw io.ReadWriter = r   //not ok
        var rw2 io.ReadWriter = new(os.File)
        var r2 io.Reader = rw2    //ok

// ReadWriter is the interface that groups the basic Read and Write methods.
type ReadWriter interface {
    Reader
    Writer
}

type ReadWriter interface {
    Read(p []byte) (n int, err error) 
    Write(p []byte) (n int, err error)
}

// illegal: Bad cannot embed itself
type Bad interface {
    Bad
}
// illegal: Bad1 cannot embed itself using Bad2
type Bad1 interface {
    Bad2
}
type Bad2 interface {
    Bad1
}

str, ok := value.(string)
if ok {
    fmt.Printf("string value is: %q\n", str)
} else {
    fmt.Printf("value is not a string\n")
}

switch x.(type) {
    // cases :
}

var value interface{} // Value provided by caller.
switch str := value.(type) {
case string:
    return str //type of str is string
case int: 
    return int //type of str is int
}

package main

import (
	"fmt"
	"reflect"
)

type State struct{}

func testnil1(a, b interface{}) bool {
	return a == b
}

func testnil2(a *State, b interface{}) bool {
	return a == b
}

func testnil3(a interface{}) bool {
	return a == nil
}

func testnil4(a *State) bool {
	return a == nil
}

func testnil5(a interface{}) bool {
	v := reflect.ValueOf(a)
	return !v.IsValid() || v.IsNil()
}

func main() {
	var a *State
	fmt.Println(testnil1(a, nil))
	fmt.Println(testnil2(a, nil))
	fmt.Println(testnil3(a))
	fmt.Println(testnil4(a))
	fmt.Println(testnil5(a))
}