account(initial_balance) {
  deposit(amount) {
    dispatch['balance']  = amount; //error message on dispatch here.
    return dispatch['balance'];//error message on dispatch here.
  }

  withdraw(amount) {
    if (amount > dispatch['balance']) { //error message on dispatch here.
      return 'Insufficient funds';
    }
    dispatch['balance'] -= amount;//error message on dispatch here.
    return dispatch['balance'];//error message on dispatch here.
  }

  var dispatch = {
    'deposit': deposit,
    'withdraw': withdraw,
    'balance': initial_balance
  };
  return dispatch;
}

withdraw(account, amount) {
  return account['withdraw'](amount);
}

deposit(account, amount) {
  return account['deposit'](amount);
}

check_balance(account) {
  return account['balance'];
}

I translated this code from python dictionaries, But in dart i am getting the following error

"Local variable dispatch cannot be referenced before it is declared.Try renaming/moving the declaration before first use so that it doesn't hide a name from enclosing scope"

Any ideas on what is causing this type of error and how i can use dictionary without having to declare it before the functions? The code works in python where i can declare dictionary in the last part of the function.

CodePudding user response：

As the error message says, dispatch must be declared before it is referenced. You can declare dispatch separately (either as an empty Map or as a late variable) before defining the local functions, and you then can add those references later.

Map<String, dynamic> account(dynamic initial_balance) {
  late Map<String, dynamic> dispatch;
  
  dynamic deposit(dynamic amount) {
    dispatch['balance']  = amount;
    return dispatch['balance'];
  }

  dynamic withdraw(dynamic amount) {
    if (amount > dispatch['balance']) {
      return 'Insufficient funds';
    }
    dispatch['balance'] -= amount;
    return dispatch['balance'];
  }

  dispatch = <String, dynamic>{
    'deposit': deposit,
    'withdraw': withdraw,
    'balance': initial_balance
  };
  return dispatch;
}