Loan type class

ClosableLoan.scala

implicit def ClosableLoan[C <: { def close(): Unit }] = new Loan[C] {

  override def using[A](closable: C)(block: C => A) = try {
    block(closable)
  } finally { closable.close }
}

gistfile1.scala

using(new FileInputStream(file)) { in =>
  // do something
}

using(Tx(conn)) { c =>
  // do transaction
}

Loan.scala

trait Loan[L] {
  def using[A](l: L)(block: L => A): A
}

def using[L: Loan, A](l: L)(block: L => A) = implicitly[Loan[L]].using(l)(block)

TransactionLoan.scala

import scalaz._, Scalaz._  // needs Scalaz 7
import java.sql.Connection

sealed trait Tx
def Tx[A](conn: Connection) = Tag[Connection, Tx](conn)

implicit object TransactionLoan extends Loan[Connection @@ Tx] {

  override def using[A](conn: Connection @@ Tx)(block: Connection @@ Tx => A) = try {
    val r = block(conn)
    conn.commit
    r
  } catch {
    case t: Throwable =>
      conn.rollback
      throw t
  }
}