Overhaul the argument parsing API

lib/argparse/types/Bool.dart

@@ -2,9 +2,13 @@ import 'package:libac_dart/argparse/Args.dart';
 
 class BoolArgument extends Argument<bool> {
   bool _value = false;
-  BoolArgument({required super.name, super.description = ""}) {
-    hasValue = false;
-    _value = true;
+  bool _hasValue = true;
+
+  BoolArgument({required super.name, bool? value = true}) {
+    if (value != null)
+      this._value = value;
+    else
+      _hasValue = false;
   }
 
   @override
@@ -21,4 +25,9 @@ class BoolArgument extends Argument<bool> {
   String toString() {
     return "BooleanArgument{ ${name}=${_value} }";
   }
+
+  @override
+  bool hasValue() {
+    return _hasValue;
+  }
 }

lib/argparse/types/Integers.dart

@@ -1,16 +1,25 @@
 import 'package:libac_dart/argparse/Args.dart';
 
 class IntegerArgument extends Argument<int> {
-  final int value;
+  int _value = 0;
+  bool _hasValue = false;
 
-  IntegerArgument(
-      {required super.name, required this.value, super.description = ""}) {
-    hasValue = value != 0;
+  IntegerArgument({required super.name, int? value}) {
+    if (value != null) {
+      this._value = value;
+      _hasValue = true;
+    } else
+      _hasValue = false;
+  }
+
+  @override
+  bool hasValue() {
+    return _hasValue;
   }
 
   @override
   int getValue() {
-    return value;
+    return _value;
   }
 
   @override
@@ -20,16 +29,25 @@ class IntegerArgument extends Argument<int> {
 
   @override
   String toString() {
-    return "IntegerArgument{ ${name}=${value} }";
+    return "IntegerArgument{ ${name}=${_value} }";
   }
 }
 
 class DoubleArgument extends Argument<double> {
-  final double value;
+  double _value = 0.0;
+  bool _hasValue = false;
 
-  DoubleArgument(
-      {required super.name, required this.value, super.description = ""}) {
-    hasValue = value != 0.0;
+  DoubleArgument({required super.name, double? value}) {
+    if (value != null) {
+      _hasValue = true;
+      _value = value;
+    } else
+      _hasValue = false;
+  }
+
+  @override
+  bool hasValue() {
+    return _hasValue;
   }
 
   @override
@@ -39,11 +57,11 @@ class DoubleArgument extends Argument<double> {
 
   @override
   double getValue() {
-    return value;
+    return _value;
   }
 
   @override
   String toString() {
-    return "DoubleArgument{ ${name}=${value} }";
+    return "DoubleArgument{ ${name}=${_value} }";
   }
 }

lib/argparse/types/String.dart

@@ -1,16 +1,25 @@
 import 'package:libac_dart/argparse/Args.dart';
 
 class StringArgument extends Argument<String> {
-  final String value;
+  String _value = "";
+  bool _hasValue = false;
 
-  StringArgument(
-      {required super.name, required this.value, super.description}) {
-    hasValue = value.isNotEmpty;
+  StringArgument({required super.name, String? value}) {
+    if (value != null) {
+      _hasValue = true;
+      _value = value;
+    } else
+      _hasValue = false;
+  }
+
+  @override
+  bool hasValue() {
+    return _hasValue;
   }
 
   @override
   String getValue() {
-    return value;
+    return _value;
   }
 
   @override
@@ -20,6 +29,6 @@ class StringArgument extends Argument<String> {
 
   @override
   String toString() {
-    return "StringArgument{ ${name}=${value} }";
+    return "StringArgument{ ${name}=${_value} }";
   }
 }