Golang: Why sql.Tx does not implement driver.Tx

Question

Why in the following example compiler says sql.Tx does not implement driver.Tx, seeing that sql.Tx does indeed fulfil the interface:

import (
    "database/sql"
    "database/sql/driver"
)


func main() {
    var myDB store = db{}
}

type store interface {
    Store(tx driver.Tx)
}

type db struct {}

func (db) Store(tx *sql.Tx) {}

type Tx interface {
    Commit() error
    Rollback() error
}

./prog.go:9:6: cannot use db{} (type db) as type store in assignment:
    db does not implement store (wrong type for Store method)
        have Store(*sql.Tx)
        want Store(driver.Tx)

https://play.golang.org/p/p3vryYI_dhV

Answer 1

Your implementation needs to match exactly, so Store() must accept a driver.TX type. Not only a *sql.Tx.

Because sql.Tx implements the driver.Tx interface it can be provided as the input.

import (
    "database/sql"
    "database/sql/driver"
)

func main() {
    var myDB store = db{}
    sqlTx := &sql.Tx{}
    myDB.Store(sqlTx)
}

type store interface {
    Store(tx driver.Tx)
}

type db struct{}

func (db) Store(tx driver.Tx) {}