d4rt

d4rt (pronounced "dart") is an interpreter and runtime for the Dart language, written in Dart.
It allows you to execute Dart code dynamically, bridge native classes, and build advanced scripting or plugin systems in your Dart/Flutter applications.

---

Features

• Dart interpreter: Run Dart code dynamically at runtime.
• Precompiled scripts & AST caching: Pre-parse and validate scripts with compile() and execute repeatedly with executeCompiled() for maximum performance.
• Execution limits & timeouts: Protect against infinite loops and runaway CPU usage with timeout and maxSteps sandbox limits.
• Interactive CLI & REPL: Run scripts directly or launch an interactive shell with dart run d4rt.
• Full generics support: Complete support for generic classes, functions, and type constraints with runtime validation.
• Type bounds checking: Enforce generic type constraints (e.g., T extends num) with dynamic resolution.
• Bridging system: Expose your own Dart/Flutter classes, enums, and methods to interpreted code.
• Async/await support: Handle asynchronous code and Futures.
• Class, enum, and extension support: Use most Dart language features, including classes, inheritance, mixins, enums, and extensions.
• Pattern matching: Support for Dart's pattern matching in switch/case and assignments.
• Runtime type validation: Validate generic type arguments and method parameters at runtime.
• Security sandboxing: Permission-based security system to restrict dangerous operations and prevent malicious code execution.
• Custom logging: Integrated, configurable logger for debugging interpreted code.
• Function argument passing: Pass positional and named arguments directly to functions via execute().
• Code introspection: Analyze Dart code structure with the analyze() method to extract metadata.
• Dynamic code evaluation: Execute code dynamically with eval() while preserving execution state.
• Extensible: Add your own bridges for custom types and native APIs.

---

Installation

Add to your pubspec.yaml:

dependencies:
  d4rt: # latest version

Then run:

dart pub get

---

Usage Example

import 'package:d4rt/d4rt.dart';

void main() {
  final code = '''
    int fib(int n) {
      if (n <= 1) return n;
      return fib(n - 1) + fib(n - 2);
    }
    main() {
      return fib(6);
    }
  ''';

  final interpreter = D4rt();
  final result = interpreter.execute(source: code);
  print('Result: $result'); // Result: 8
}

Advanced Features

Function Argument Passing

Pass positional and named arguments directly to functions:

final interpreter = D4rt();

final result = interpreter.execute(
  source: '''
    String greet(String name, {String greeting = "Hello"}) {
      return "\$greeting, \$name!";
    }
  ''',
  name: 'greet',
  positionalArgs: ['Alice'],
  namedArgs: {'greeting': 'Hi'},
);
print(result); // Hi, Alice!

Interpreted function invocation

Invoke interpreted functions from host dart code:

final interpreter = D4rt();

final interpretedFn = interpreter.execute( 
  source: '''
      int sum(int a, int b) => a+b;
      main() => sum;
  '''
);

final result = d4rt.invokeInterpretedFunction(interpretedFn, [1,2]);
print(result); // 3

Promote interpreted functions to host functions to better integration:

final interpreter = D4rt();

final interpretedFn = interpreter.execute( 
  source: '''
      int sum(int a, int b) => a+b;
      main() => sum;
  '''
);

T Function(A, B) bindFunction2<T, A, B>(D4rt d, InterpretedFunction fn) {
  return (A a, B b) => d.invokeInterpretedFunction(fn, [a, b]);
}

final nativeFn = bindFunction2(interpreter,interpretedFn);
print( nativeFn(1,2) ); // 3

Note that it is possible to pass InterpretedFunction as argumento to invokeInterpretedFunction, but pass a native function it is not currently supported.

Code Introspection

Analyze Dart code structure without execution:

final interpreter = D4rt();

final analysis = interpreter.analyze('''
  class User {
    String name;
    int age;
    User(this.name, this.age);
  }
  
  int getAge(User user) => user.age;
''');

// Access metadata about functions, classes, variables, etc.
print(analysis.functions['getAge']?.parameters);
print(analysis.classes['User']?.constructors);

Dynamic Code Evaluation

Execute code dynamically while preserving execution state:

final interpreter = D4rt();

interpreter.execute(source: 'int x = 10;');
final result = interpreter.eval('x + 5'); // Returns 15

Precompiled Scripts & AST Caching

For high-performance scenarios where the same script is executed multiple times, precompile the AST once to avoid re-parsing overhead:

final d4rt = D4rt();

// Compile once
final script = d4rt.compile(source: '''
  int multiply(int a, int b) => a * b;
''');

// Execute repeatedly with zero parsing overhead
final r1 = d4rt.executeCompiled(script, name: 'multiply', positionalArgs: [6, 7]); // 42
final r2 = d4rt.executeCompiled(script, name: 'multiply', positionalArgs: [10, 5]); // 50

You can also enable automatic AST caching for repeated source strings:

final d4rt = D4rt(enableAstCache: true);
// Subsequent execute() calls with identical source strings will reuse cached ASTs

Execution Limits & Timeout Protection

Protect against infinite loops and runaway CPU usage by setting maximum step quotas or execution timeouts:

final d4rt = D4rt();

try {
  d4rt.execute(
    source: '''
      void main() {
        while (true) { /* infinite loop */ }
      }
    ''',
    maxSteps: 1000, // Maximum execution steps
    timeout: Duration(milliseconds: 500), // Maximum execution duration
  );
} on ExecutionLimitException catch (e) {
  print('Step limit exceeded: $e');
} on ExecutionTimeoutException catch (e) {
  print('Timed out: $e');
}

Command-Line Interface (CLI) & Interactive REPL

d4rt includes a built-in CLI runner and an interactive REPL shell:

# Run a Dart script file directly
dart run d4rt path/to/script.dart [args...]

# Start an interactive REPL session
dart run d4rt repl
# or simply
dart run d4rt

Inside the REPL:

==============================================
  d4rt v0.2.2 - Interactive Dart REPL
  Type :help for help, :exit or Ctrl+C to quit
==============================================

d4rt> var x = 10;
d4rt> int double(int n) => n * 2;
d4rt> double(x)
=> 20
d4rt> :exit
Goodbye!

Security Sandboxing

d4rt includes a comprehensive permission-based security system to prevent malicious code execution. By default, access to dangerous modules like dart:io and dart:isolate is blocked unless explicitly granted.

Granting Permissions

import 'package:d4rt/d4rt.dart';

void main() {
  final interpreter = D4rt();

  // Grant filesystem access
  interpreter.grant(FilesystemPermission.any);

  // Grant network access
  interpreter.grant(NetworkPermission.any);

  // Grant process execution
  interpreter.grant(ProcessRunPermission.any);

  // Grant isolate operations
  interpreter.grant(IsolatePermission.any);

  // Now execute code that uses dangerous operations
  final result = interpreter.execute(source: '''
    import 'dart:io';
    import 'dart:isolate';

    void main() {
      // This code can now access filesystem, network, etc.
      print('Secure execution with granted permissions');
    }
  ''');
}

Permission Types

• FilesystemPermission: Controls file and directory operations

  • FilesystemPermission.any - Allow all filesystem operations
  • FilesystemPermission.read - Allow read-only operations
  • FilesystemPermission.write - Allow write operations
  • FilesystemPermission.path('/specific/path') - Allow operations on specific paths

• NetworkPermission: Controls network operations

  • NetworkPermission.any - Allow all network operations
  • NetworkPermission.connect('host:port') - Allow connections to specific hosts

• ProcessRunPermission: Controls process execution

  • ProcessRunPermission.any - Allow execution of any command
  • ProcessRunPermission.command('specific-command') - Allow execution of specific commands

• IsolatePermission: Controls isolate creation and communication

  • IsolatePermission.any - Allow all isolate operations

Permission Management

final interpreter = D4rt();

// Grant permissions
interpreter.grant(FilesystemPermission.any);

// Check permissions
if (interpreter.hasPermission(FilesystemPermission.any)) {
  print('Filesystem access granted');
}

// Revoke permissions
interpreter.revoke(FilesystemPermission.any);

Filesystem Module Imports

Use basePath together with allowFileSystemImports: true when interpreted code imports local files from disk.

final interpreter = D4rt();
interpreter.grant(FilesystemPermission.readPath('/path/to/project/lib'));

final result = interpreter.execute(
  source: '''
    import './utils.dart';
    String main() => greetFromUtils();
  ''',
  basePath: '/path/to/project/lib',
  allowFileSystemImports: true,
);

Rules:

• Relative filesystem imports require basePath.
• Filesystem modules are blocked unless allowFileSystemImports is enabled.
• Reading modules from disk also requires a matching FilesystemPermission.
• Missing local files raise a SourceCodeException with the resolved filesystem path.

Bridging Native Classes & Enums

d4rt provides a powerful bridging system that allows you to automate the process of exposing your Dart and Flutter classes, enums, and functions to the interpreter using build_runner.

Automated Bridge Generation (Recommended)

1. Add build_runner and d4rt dev dependencies:

   dev_dependencies:
     build_runner: ^2.4.0
   

2. Annotate your classes or enums with @D4rtBridge():

   import 'package:d4rt/d4rt.dart';
   part 'color.g.dart';
   @D4rtBridge(libraryUri: 'package:app/color.dart')
   class Color {
     final int value;
     const Color(this.value);
        
     static const Color black = Color(0xFF000000);
        
     int get red => (value >> 16) & 0xFF;
   }
   

3. Run the code generator:

   dart run build_runner build
   

   This will generate a .g.dart file containing the bridge definitions and an automatic registration function.

4. Register the bridges with the interpreter:

   import 'package:d4rt/d4rt.dart';
   import 'color.dart'; // Import the generated file
   
   void main() {
     final interpreter = D4rt();
        
     // Register all bridges in the file with a single line:
     registerColorBridges(interpreter);
        
     // Now 'Color' is available in the interpreter under 'package:app/color.dart'
   }
   

Manual Bridge Definition

If you prefer to define bridges manually (without code generation), you can use the BridgedClass and BridgedEnumDefinition classes:

Bridge a Dart Class (Manual)

import 'package:d4rt/d4rt.dart';

class MyClass {
  int value;
  MyClass(this.value);
  int doubleValue() => value * 2;
}

final myClassBridge = BridgedClass(
  nativeType: MyClass,
  name: 'MyClass',
  constructors: {
    '': (InterpreterVisitor visitor, List<Object?> positionalArgs, Map<String, Object?> namedArgs) {
      if (positionalArgs.length == 1 && positionalArgs[0] is int) {
        return MyClass(positionalArgs[0] as int);
      }
      throw ArgumentError('MyClass constructor expects one integer argument.');
    },
  },
  methods: {
    'doubleValue': (InterpreterVisitor visitor, Object target, List<Object?> positionalArgs, Map<String, Object?> namedArgs) {
      if (target is MyClass) {
        return target.doubleValue();
      }
      throw TypeError();
    },
  },
  getters: {
    'value': (InterpreterVisitor? visitor, Object target) {
      if (target is MyClass) {
        return target.value;
      }
      throw TypeError();
    },
  },
);

void main() {
  final interpreter = D4rt();
  interpreter.registerBridgedClass(myClassBridge, 'package:example/my_class_library.dart');

  final code = '''
    import 'package:example/my_class_library.dart';

    main() {
      var obj = MyClass(21);
      return obj.doubleValue();
    }
  ''';

  final result = interpreter.execute(source: code);
  print(result); // 42
}

Bridge a Dart Enum (Manual)

import 'package:d4rt/d4rt.dart';

enum Color { red, green, blue }

final colorEnumBridge = BridgedEnumDefinition<Color>(
  name: 'Color',
  values: Color.values,
);

void main() {
  final interpreter = D4rt();
  interpreter.registerBridgedEnum(colorEnumBridge, 'package:example/my_enum_library.dart');

  final code = '''
    import 'package:example/my_enum_library.dart';

    main() {
      var favoriteColor = Color.green;
      print('My favorite color is \${favoriteColor.name}');
      return favoriteColor.index;
    }
  ''';

  final result = interpreter.execute(source: code);
  print(result); // 1
}

Advanced Annotation Options

The @D4rtBridge annotation provides several configuration parameters:

• libraryUri: The namespace where the class will be registered (e.g., 'package:app/color.dart').
• includePrivate: Whether to generate bridges for private members (default: false).
• bridgeName: A custom variable name for the generated bridge (useful for avoiding name collisions).

Example:

@D4rtBridge(
  libraryUri: 'package:app/models.dart',
  includePrivate: true,
  bridgeName: 'customUserBridge',
)
class User { ... }

---

Supported Features

Feature	Status / Notes
Classes & Inheritance	✅ Full support (abstract, inheritance, mixins, interfaces, sealed, base, final)
Enums	✅ Full support (fields, methods, static, named values, index, name)
Mixins	✅ Supported (declaration, application, on clause, constraints)
Extensions	✅ Supported (methods, getters, setters, operators)
Async/await	✅ Supported (async functions, await, Futures)
Pattern matching	✅ Supported (switch/case, if-case, destructuring, list/map/record patterns)
Collections (List, Map, Set)	✅ Supported (literals, spread, if/for, nested, null-aware, records)
Top-level functions	✅ Supported (named, anonymous, closures, nested)
Getters/Setters	✅ Supported (instance, static, extension, bridge)
Static members	✅ Supported (fields, methods, getters/setters, bridge)
Switch/case	✅ Supported (classic, pattern, default, fallthrough, exhaustive checks)
Try/catch/finally	✅ Supported (multiple catch, on/type, rethrow, stacktrace)
Imports	✅ Supported (URIs, show/hide clauses for libraries defined in sources)
Generics	✅ Full support (generic classes/functions, type constraints, runtime validation)
Extension types	✅ Full support (representation fields, constructors, methods)
Precompiled scripts & AST Cache	✅ Full support (compile, executeCompiled, AST caching)
Execution limits & Timeouts	✅ Full support (timeout, maxSteps, sandbox exceptions)
Operator overloading	✅ Full support
FFI	🚫 Not supported
Isolates (dart:isolate)	✅ Full support
Developer (dart:developer)	✅ Full support (Timeline, UserTag, Service, log, debugger, inspect)
Reflection/Mirrors	🚫 Not supported
Records	✅ Supported (positional, named, pattern matching)
String interpolation	✅ Supported
Cascade notation (..)	✅ Supported
Null safety	✅ Supported (null-aware ops, checks, patterns)
Type tests (is, as)	✅ Supported
Exception handling	✅ Supported (throw, rethrow, custom errors)

See the documentation for details and limitations.

---

Limitations

• Operator overloading is partially supported (via extensions, not via class operator methods).
• Some advanced Dart features (FFI, mirrors) are not available.
• The interpreter is not a full Dart VM: some language features may behave differently.

---

Documentation

• API Reference
• Bridging Guide
• Supported Features
• Examples

---

Contributing

Contributions are welcome!
Feel free to open issues, suggest features, or submit pull requests.

---

License

MIT License. See LICENSE.

---

About the Name

d4rt is a play on the word "dart", using "4" as a stylized "A".
It is pronounced exactly like "dart".