dart_qvariant

A Qt-style, immutable variant type wrapper for Dart, providing smart casting and safe typed access to dynamic values.

Inspired by Qt's QVariant, this package lets you easily work with values of unknown or mixed types (e.g. from JSON or loosely typed data sources) with convenient conversions and null safety.

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Features

• Immutable wrapper around any dynamic value
• Typed getters with automatic safe conversions:
  • toInt(), toDouble(), toBoolean(), toText(), toNumeric(), toDateTime()
• Null safety and graceful fallback (returns null when conversion fails)
• Customizable numeric string formatting with rounding
• Simple, concise API inspired by Qt's QVariant

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Installation

Add to your pubspec.yaml:

dart pub add dart_qvariant

or

flutter pub add dart_qvariant

Then run:

dart pub get

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Usage

Import the package:

import 'package:dart_qvariant/dart_qvariant.dart';

Create a Variant wrapping any value:

final v1 = Variant("42");
final v2 = Variant(3.1415);
final v3 = Variant(true);
final v4 = Variant(null);
final v5 = Variant("2024-06-04T18:00:00");

Type checks

print(v1.isString);  // true
print(v2.isDouble);  // true
print(v3.isBool);    // true
print(v4.isNull);    // true
print(v5.isString);  // true

Conversions

print(v1.toInt());      // 42 (int)
print(v1.toDouble());   // 42.0 (double)
print(v2.toInt());      // 3 (int)
print(v3.toBoolean());  // true (bool)
print(v4.toText());     // null (String?)
print(v5.toDateTime()?.toIso8601String()); // 2024-06-04T18:00:00.000

If conversion fails, methods return null:

final v = Variant("not a number");
print(v.toInt());       // null
print(v.toDouble());    // null
print(v.toBoolean());   // false (since string != 'true')

Numeric string formatting

You can get a nicely formatted numeric string with rounding:

final v = Variant("3.1415926535");
print(v.toNumericString());           // "3.14" (default 2 decimals)
print(v.toNumericString(roundCount: 4)); // "3.1416"

For booleans, it returns "true" or "false" strings:

print(Variant(true).toNumericString());  // "true"
print(Variant(false).toNumericString()); // "false"

DateTime parsing

You can parse dates from ISO8601 strings or DateTime objects:

final dt1 = Variant("2024-06-04T18:00:00Z").toDateTime();
final dt2 = Variant(DateTime.now()).toDateTime(toLocal: true);

print(dt1);  // Parsed UTC date
print(dt2);  // Local date time

Returns null if parsing fails:

print(Variant("invalid-date").toDateTime());  // null

Useful in JSON or loosely typed data handling

final Map<String, dynamic> json = {
  'id': '123',
  'price': '99.95',
  'active': 'true',
  'created': '2024-01-01T12:00:00Z',
};

final id = Variant(json['id']).toInt();
final price = Variant(json['price']).toDouble();
final active = Variant(json['active']).toBoolean();
final created = Variant(json['created']).toDateTime();

print('ID: \$id');           // 123
print('Price: \$price');     // 99.95
print('Active: \$active');   // true
print('Created: \$created'); // 2024-01-01 12:00:00.000Z