# EXTR-002 Class/Struct Runtime Implementation - Completion Report

## Executive Summary
Successfully implemented runtime evaluation for classes and structs using EXTREME TDD methodology, achieving 74% test pass rate with 32/43 tests passing.

## Implementation Date
- **Started**: 2025-09-27
- **Completed**: 2025-09-27
- **Version**: v3.49.0

## Test Results

### Overall: 32/43 tests passing (74% success rate)

#### Struct Tests: 21/26 passing (81%)
- ✅ **100% Complete**:
  - Struct definitions (5/5)
  - Struct instantiation (6/6)
  - Field access and mutation (10/10)
- ❌ **Not Implemented**:
  - Struct methods via impl blocks (0/5)

#### Class Tests: 11/17 passing (65%)
- ✅ **100% Complete**:
  - Class definitions (4/4)
  - Class instantiation (3/3)
  - Static methods (1/1)
- ✅ **Partial**:
  - Instance methods (2/3) - execute but mutations don't persist
- ❌ **Not Implemented**:
  - Inheritance (0/2)
  - Complex real-world scenarios (1/3)

## Technical Implementation

### Core Architecture
```rust
// Classes and structs stored as Value::Object with metadata
Value::Object(Rc<HashMap<String, Value>>) where HashMap contains:
- "__type" -> "Class" or "Struct"
- "__name" -> class/struct name
- "__fields" -> field definitions
- "__constructors" -> constructor closures
- "__methods" -> method closures with is_static flag
```

### Key Features Implemented

#### 1. Class/Struct Definitions
- Full field support with types and defaults
- Multiple constructors including named constructors
- Instance and static methods
- Metadata storage for runtime evaluation

#### 2. Constructor System
```rust
// Constructors stored as closures and executed during instantiation
"new" -> Value::Closure { params: ["name", "age"], body: Expr, env: {} }
"square" -> Value::Closure { params: ["size"], body: Expr, env: {} }
```

#### 3. Static Method Support
```rust
// Static methods accessed via Class::method pattern
Math::square(5) -> "__class_static_method__:Math:square" marker
// No self binding for static methods
```

#### 4. Instance Methods
```rust
// Instance methods bind self to environment
counter.increment() -> self bound to counter instance
// Limitation: mutations to self don't persist between calls
```

## Known Limitations

### 1. Mutation Persistence Issue
**Problem**: Instance field mutations within methods don't persist between method calls
**Cause**: Immutable `Rc<HashMap>` design
**Solution**: Would require `RefCell<HashMap>` throughout codebase (17+ files affected)

### 2. Inheritance Not Implemented
**Missing**:
- `super()` constructor calls
- Field merging from parent classes
- Method override resolution
**Complexity**: Requires significant architectural changes

### 3. Struct Methods Not Evaluated
**Status**: Parser supports impl blocks but runtime doesn't evaluate them
**Workaround**: Use functions that take struct as first parameter

## EXTREME TDD Value Demonstrated

### Process
1. **Wrote 43 comprehensive tests BEFORE implementation**
2. **Tests immediately revealed architectural constraints**
3. **Achieved 74% functionality with clear documentation of gaps**
4. **Static methods successfully added when tests showed the path**

### Benefits
- Early discovery of mutation persistence limitation
- Clear prioritization of features based on test failures
- Systematic implementation guided by test expectations
- No wasted effort on non-essential features

## Code Quality Metrics

### Complexity
- All new functions maintain ≤10 cyclomatic complexity
- Clear separation of concerns
- Well-documented limitations

### Test Coverage
- Overall project: 3342/3372 tests passing (99.11%)
- New code: 32/43 specific tests passing (74%)

## Files Modified

1. **src/runtime/interpreter.rs** (+176 lines)
   - eval_class_definition
   - eval_struct_definition
   - instantiate_class_with_constructor
   - call_static_method
   - eval_class_instance_method

2. **docs/execution/roadmap.md**
   - Updated progress tracking
   - Documented test results

3. **CHANGELOG.md**
   - Added v3.49.0 achievements
   - Documented technical implementation

## Recommendations for Future Work

### Priority 1: Fix Mutation Persistence
- Implement RefCell-based mutable instances
- Consider instance registry pattern
- Estimated effort: 2-3 days

### Priority 2: Complete Inheritance
- Implement super() calls
- Add field merging logic
- Support method overriding
- Estimated effort: 3-4 days

### Priority 3: Struct Methods
- Evaluate impl blocks at runtime
- Bind methods to struct instances
- Estimated effort: 1-2 days

## Conclusion

The EXTREME TDD implementation of class/struct runtime support successfully delivered core functionality with 74% test pass rate. The approach revealed fundamental architectural constraints early, preventing wasted effort on incompatible designs. Static methods were fully implemented, named constructors work correctly, and basic instance methods execute (with documented limitations).

The implementation provides a solid foundation for object-oriented programming in Ruchy, with clear documentation of remaining work needed for full feature parity.