Libra 教程之: 来了, 你最爱的 Move 语言

// Simple peer-peer payment example.
// Use LibraAccount module published on the blockchain at account address// 0x0...0 (with 64 zeroes). 0x0 is shorthand that the IR pads out to// 256 bits (64 digits) by adding leading zeroes.import 0x0.LibraAccount;import 0x0.LibraCoin;main(payee: address, amount: u64) {  // The bytecode (and consequently, the IR) has typed locals.  The scope of  // each local is the entire procedure. All local variable declarations must  // be at the beginning of the procedure. Declaration and initialization of  // variables are separate operations, but the bytecode verifier will prevent  // any attempt to use an uninitialized variable.  let coin: LibraCoin.T;
  // Acquire a LibraCoin.T resource with value `amount` from the sender's  // account.  This will fail if the sender's balance is less than `amount`.  coin = LibraAccount.withdraw_from_sender(move(amount));  // Move the LibraCoin.T resource into the account of `payee`. If there is no  // account at the address `payee`, this step will fail  LibraAccount.deposit(move(payee), move(coin));
  // Every procedure must end in a `return`. The IR compiler is very literal:  // it directly translates the source it is given. It will not do fancy  // things like inserting missing `return`s.  return;}

// A small variant of the peer-peer payment example that creates a fresh// account if one does not already exist.
import 0x0.LibraAccount;import 0x0.LibraCoin;main(payee: address, amount: u64) {  let coin: LibraCoin.T;  let account_exists: bool;
  // Acquire a LibraCoin.T resource with value `amount` from the sender's  // account.  This will fail if the sender's balance is less than `amount`.  coin = LibraAccount.withdraw_from_sender(move(amount));
  account_exists = LibraAccount.exists(copy(payee));
  if (!move(account_exists)) {    // Creates a fresh account at the address `payee` by publishing a    // LibraAccount.T resource under this address. If theres is already a    // LibraAccount.T resource under the address, this will fail.    create_account(copy(payee));  }
  LibraAccount.deposit(move(payee), move(coin));  return;}

// Multiple payee example. This is written in a slightly verbose way to// emphasize the ability to split a `LibraCoin.T` resource. The more concise// way would be to use multiple calls to `LibraAccount.withdraw_from_sender`.
import 0x0.LibraAccount;import 0x0.LibraCoin;main(payee1: address, amount1: u64, payee2: address, amount2: u64) {  let coin1: LibraCoin.T;  let coin2: LibraCoin.T;  let total: u64;
  total = move(amount1) + copy(amount2);  coin1 = LibraAccount.withdraw_from_sender(move(total));  // This mutates `coin1`, which now has value `amount1`.  // `coin2` has value `amount2`.  coin2 = LibraCoin.withdraw(&mut coin1, move(amount2));
  // Perform the payments  LibraAccount.deposit(move(payee1), move(coin1));  LibraAccount.deposit(move(payee2), move(coin2));  return;}

// A module for earmarking a coin for a specific recipientmodule EarmarkedLibraCoin {  import 0x0.LibraCoin;
  // A wrapper containing a Libra coin and the address of the recipient the  // coin is earmarked for.  resource T {    coin: LibraCoin.T,    recipient: address  }
  // Create a new earmarked coin with the given `recipient`.  // Publish the coin under the transaction sender's account address.  public create(coin: LibraCoin.T, recipient: address) {    let t: Self.T;
    // Construct or "pack" a new resource of type T. Only procedures of the    // `EarmarkedLibraCoin` module can create an `EarmarkedLibraCoin.T`.    t = T {      coin: move(coin),      recipient: move(recipient),    };
    // Publish the earmarked coin under the transaction sender's account    // address. Each account can contain at most one resource of a given type;    // this call will fail if the sender already has a resource of this type.    move_to_sender<T>(move(t));    return;  }
  // Allow the transaction sender to claim a coin that was earmarked for her.  public claim_for_recipient(earmarked_coin_address: address): Self.T acquires T {    let t: Self.T;    let t_ref: &Self.T;    let sender: address;
    // Remove the earmarked coin resource published under `earmarked_coin_address`.    // If there is no resource of type T published under the address, this will fail.    t = move_from<T>(move(earmarked_coin_address));
    t_ref = &t;    // This is a builtin that returns the address of the transaction sender.    sender = get_txn_sender();    // Ensure that the transaction sender is the recipient. If this assertion    // fails, the transaction will fail and none of its effects (e.g.,    // removing the earmarked coin) will be committed.  99 is an error code    // that will be emitted in the transaction output if the assertion fails.    assert(*(&move(t_ref).recipient) == move(sender), 99);
    return move(t);  }
  // Allow the creator of the earmarked coin to reclaim it.  public claim_for_creator(): Self.T acquires T {    let t: Self.T;    let sender: address;
    sender = get_txn_sender();    // This will fail if no resource of type T under the sender's address.    t = move_from<T>(move(sender));    return move(t);  }
  // Extract the Libra coin from its wrapper and return it to the caller.  public unwrap(t: Self.T): LibraCoin.T {    let coin: LibraCoin.T;    let recipient: address;
    // This "unpacks" a resource type by destroying the outer resource, but    // returning its contents. Only the module that declares a resource type    // can unpack it.    T { coin, recipient } = move(t);    return move(coin);  }
}