为什么在golang中仅初始化定义中的一个变量会失败

In calling a library function with the following signature:

func New() (*sql.DB, Sqlmock, error)

like this:

suite.db, suite.mock, err := sqlmock.New() // inside a suite method

I get error

expected identifier on left side of :=

However, when I change to this

var err error
suite.db, suite.mock, err = sqlmock.New()

:=