Dart mode

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import 'dart:math' show Random;
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​
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void main() {
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  print(new Die(n: 12).roll());
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}
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​
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// Define a class.
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class Die {
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  // Define a class variable.
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  static Random shaker = new Random();
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​
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  // Define instance variables.
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  int sides, value;
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​
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  // Define a method using shorthand syntax.
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  String toString() => '$value';
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​
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  // Define a constructor.
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  Die({int n: 6}) {
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    if (4 <= n && n <= 20) {
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      sides = n;
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    } else {
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      // Support for errors and exceptions.
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      throw new ArgumentError(/* */);
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    }
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  }
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​
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  // Define an instance method.
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  int roll() {
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    return value = shaker.nextInt(sides) + 1;
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  }
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}
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​