如何解决Rust区块链智能合约中的'[E0277]:类型'[BBalance]'无法通过'String'错误进行索引?

我正在用铁锈写calculate_balance_changes函数。 但也有一些错误:

error[E0277]: the type `[Balance]` cannot be indexed by `String`
--> src/main.rs:126:30
    |
126 |                 new_balances[input.address].coins.push(Coin {
    |                              ^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
    |
= help: the trait `SliceIndex<[Balance]>` is not implemented for `String`
= note: required for `Vec<Balance>` to implement `Index<String>`

error[E0277]: the type `[Balance]` cannot be indexed by `String`
--> src/main.rs:138:26
    |
138 |             new_balances[definition.issuer].coins.push(Coin {
    |                          ^^^^^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
    |
= help: the trait `SliceIndex<[Balance]>` is not implemented for `String`
= note: required for `Vec<Balance>` to implement `Index<String>`

error[E0277]: the type `[Balance]` cannot be indexed by `String`
--> src/main.rs:149:34
    |
149 |             if original_balances[input.address].coins
    |                                  ^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
    |
= help: the trait `SliceIndex<[Balance]>` is not implemented for `String`
= note: required for `Vec<Balance>` to implement `Index<String>`

For more information about this error, try `rustc --explain E0277`.
warning: `rust-task` (bin "rust-task") generated 1 warning
error: could not compile `rust-task` due to 3 previous errors; 1 warning emitted

计算余额变化。