Transient storage

(* Transient storage (EIP-1153) lasts for one transaction: shared by every call in
   it, cleared when it ends, and cheap. It is read and written with TLOAD/TSTORE. *)
 
interface Callback is {
  function onFlash(amount : uint);
}
 
error NotInFlash;
 
transient storage flash is record {
  active : bool;
  lent : uint;
}
 
storage is record {
  totalLent : uint;
}
 
external function lend(const to : Callback; const amount : uint) is {
  flash.active := true;
  flash.lent := amount;
  storage.totalLent := storage.totalLent + amount;
  defer to.onFlash(amount);
}
 
(* Called back by the borrower during `lend`'s deferred call. *)
external view function currentLoan() : uint
  raises NotInFlash
is {
  assert(flash.active, NotInFlash);
} with flash.lent