io
├── example_test.go
├── io.go
├── io_test.go
├── ioutil
│   ├── example_test.go
│   ├── ioutil.go
│   ├── ioutil_test.go
│   ├── tempfile.go
│   ├── tempfile_test.go
│   └── testdata
│       └── hello
├── multi.go
├── multi_test.go
├── pipe.go
└── pipe_test.go

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

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

type Closer interface {
    Close() error
}

Package io provides basic interfaces to I/O primitives.
Its primary job is to wrap existing implementations of such primitives, such as those in package os, into shared public interfaces that abstract the functionality, plus some other related primitives.

Package ioutil implements some I/O utility functions.

r := strings.NewReader("Go is a general-purpose language designed with systems programming in mind.")

b, err := ioutil.ReadAll(r)
if err != nil {
    log.Fatal(err)
}

fmt.Printf("%s", b)

io // 抽象
├── example_test.go
├── io.go
├── io_test.go
├── ioutil // 具象
│   ├── example_test.go
│   ├── ioutil.go
│   ├── ioutil_test.go
│   ├── tempfile.go
│   ├── tempfile_test.go
│   └── testdata
│       └── hello
├── multi.go
├── multi_test.go
├── pipe.go
└── pipe_test.go

sql/
├── convert.go
├── convert_test.go
├── ctxutil.go
├── doc.txt
├── driver
│   ├── driver.go
│   ├── types.go
│   └── types_test.go
├── example_test.go
├── fakedb_test.go
├── sql.go
└── sql_test.go

func Open(driverName, dataSourceName string) (*DB, error) {
    driversMu.RLock()
    driveri, ok := drivers[driverName]
    driversMu.RUnlock()
    if !ok {
        return nil, fmt.Errorf("sql: unknown driver %q (forgotten import?)", driverName)
    }

    if driverCtx, ok := driveri.(driver.DriverContext); ok {
        connector, err := driverCtx.OpenConnector(dataSourceName)
        if err != nil {
            return nil, err
        }
        return OpenDB(connector), nil
    }

    return OpenDB(dsnConnector{dsn: dataSourceName, driver: driveri}), nil
}

type Driver interface {
    // Open returns a new connection to the database.
    // The name is a string in a driver-specific format.
    //
    // Open may return a cached connection (one previously
    // closed), but doing so is unnecessary; the sql package
    // maintains a pool of idle connections for efficient re-use.
    //
    // The returned connection is only used by one goroutine at a
    // time.
    Open(name string) (Conn, error)
}

func init() {
    sql.Register("mysql", &MySQLDriver{})
}

sql/ // 具象
├── convert.go
├── convert_test.go
├── ctxutil.go
├── doc.txt
├── driver // 抽象
│   ├── driver.go
│   ├── types.go
│   └── types_test.go
├── example_test.go
├── fakedb_test.go
├── sql.go
└── sql_test.go