golang---impl快速实现Interface

快速实现golang interface

golang中的interface提供了一种非常方便的方式来达到代码重用的目的。
几乎大部分的项目中都会用到interface,在日常工作中，为了实现某个interface,
我发现我也在一直不断的查询GoDocs,只有不断去查，才能知道这个interface中
有哪些方法，这无疑是非常浪费时间的。

例如，为了让我的结构体是可hash的，实现一个hash接口是非常常见的操作。以下是hash
的GoDocs:

type Hash interface {
    // Write (via the embedded io.Writer interface) adds more data to the running hash.
    // It never returns an error.
    io.Writer

    // Sum appends the current hash to b and returns the resulting slice.
    // It does not change the underlying hash state.
    Sum(b []byte) []byte

    // Reset resets the Hash to its initial state.
    Reset()

    // Size returns the number of bytes Sum will return.
    Size() int

    // BlockSize returns the hash's underlying block size.
    // The Write method must be able to accept any amount
    // of data, but it may operate more efficiently if all writes
    // are a multiple of the block size.
    BlockSize() int
}

为了实现 hash 接口，我们需要同时实现上述五个方法。

今天我来给大家介绍一种快速实现一个接口的方法。

Impl可以自动的实现一个接口，这非常有用。

如何使用呢？ 执行以一下命令即可：
impl <struct-name> <intreface-name>

还是以hash这个结构体为例，具体看一下如何使用impl。
impl Foo hash.Hash

输出：

func (Foo) Write(p []byte) (n int, err error) {
        panic("not implemented") // TODO: Implement
}

// Sum appends the current hash to b and returns the resulting slice.
// It does not change the underlying hash state.
func (Foo) Sum(b []byte) []byte {
        panic("not implemented") // TODO: Implement
}

// Reset resets the Hash to its initial state.
func (Foo) Reset() {
        panic("not implemented") // TODO: Implement
}

// Size returns the number of bytes Sum will return.
func (Foo) Size() int {
        panic("not implemented") // TODO: Implement
}

// BlockSize returns the hash's underlying block size.
// The Write method must be able to accept any amount
// of data, but it may operate more efficiently if all writes
// are a multiple of the block size.
func (Foo) BlockSize() int {
        panic("not implemented") // TODO: Implement
}

执行完上面的命令后，我们没有必要再去不断查询hash的DoDocs去看如何实现一个接口了。

想像一下，如果后面我们需要为Foo结构体实现一个新的接口sortable,将会怎么样呢？同样的
我们也可以使用impl来实现sort的interface，如下：
impl Foo sort.interface

输出：

// Len is the number of elements in the collection.
func (Foo) Len() int {
        panic("not implemented") // TODO: Implement
}

// Less reports whether the element with
// index i should sort before the element with index j.
func (Foo) Less(i int, j int) bool {
        panic("not implemented") // TODO: Implement
}

// Swap swaps the elements with indexes i and j.
func (Foo) Swap(i int, j int) {
        panic("not implemented") // TODO: Implement
}

impl不但可以实现标准库中定义的接口，同样的，它也能实现我们自定义的接口。例如：go-mysql
提供了一个管理mysql数据库的强大的工具集。下面我们为其中的"Handler"接口做一个快速实现：

$ go get github.com/siddontang/go-mysql/server
$ impl Foo server.Handler

输出：

//handle COM_INIT_DB command, you can check whether the dbName is valid, or other.
func (Foo) UseDB(dbName string) error {
        panic("not implemented") // TODO: Implement
}

//handle COM_QUERY command, like SELECT, INSERT, UPDATE, etc...
//If Result has a Resultset (SELECT, SHOW, etc...), we will send this as the response, otherwise, we will send Result
func (Foo) HandleQuery(query string) (*server.Result, error) {
        panic("not implemented") // TODO: Implement
}

//handle COM_FILED_LIST command
func (Foo) HandleFieldList(table string, fieldWildcard string) ([]*server.Field, error) {
        panic("not implemented") // TODO: Implement
}

//handle COM_STMT_PREPARE, params is the param number for this statement, columns is the column number
//context will be used later for statement execute
func (Foo) HandleStmtPrepare(query string) (params int, columns int, context interface{}, err error) {
        panic("not implemented") // TODO: Implement
}

//handle COM_STMT_EXECUTE, context is the previous one set in prepare
//query is the statement prepare query, and args is the params for this statement
func (Foo) HandleStmtExecute(context interface{}, query string, args []interface{}) (*server.Result, error) {
        panic("not implemented") // TODO: Implement
}

//handle COM_STMT_CLOSE, context is the previous one set in prepare
//this handler has no response
func (Foo) HandleStmtClose(context interface{}) error {
        panic("not implemented") // TODO: Implement
}

//handle any other command that is not currently handled by the library,
//default implementation for this method will return an ER_UNKNOWN_ERROR
func (Foo) HandleOtherCommand(cmd byte, data []byte) error {
        panic("not implemented") // TODO: Implement
}

是不是很有用呢？