CODESAMPLE
Self-contained Systems - Dart
The Self-Contained System pattern focuses on encapsulating all dependencies within a single unit (like a class or function). This eliminates external dependencies, making the system portable, testable, and easier to reason about. It promotes loose coupling and simplifies deployments.
Here, we implement a simple calculator as a self-contained system using a class. All calculator logic, including parsing and performing operations, is encapsulated within the Calculator class, without reliance on external state or libraries beyond Dart’s core functionality. This illustrates how to achieve modularity and reduce dependencies, fitting Dart’s class-based structure and promoting code organization. The calculate method handles all operation logic, ensuring a clear entry point and contained behavior.
// main.dart
class Calculator {
String calculate(String expression) {
try {
// Basic parsing and evaluation. Could use a more robust library
// if complexity increased, but keeping it contained.
final List<String> parts = expression.split(' ');
if (parts.length != 3) {
return "Invalid expression";
}
final num operand1 = double.parse(parts[0]);
final String operator = parts[1];
final num operand2 = double.parse(parts[2]);
num result;
switch (operator) {
case '+':
result = operand1 + operand2;
break;
case '-':
result = operand1 - operand2;
break;
case '*':
result = operand1 * operand2;
break;
case '/':
if (operand2 == 0) {
return "Division by zero";
}
result = operand1 / operand2;
break;
default:
return "Invalid operator";
}
return result.toString();
} catch (e) {
return "Invalid input";
}
}
}
void main() {
final calculator = Calculator();
print(calculator.calculate('10 + 5'));
print(calculator.calculate('20 / 4'));
print(calculator.calculate('3 * 7'));
print(calculator.calculate('12 - 6'));
print(calculator.calculate('5 + ')); // Invalid
print(calculator.calculate('10 / 0')); // Division by zero
}