Start C++ rewrite.

docs/CONSTANTS_REFACTORING.md

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+# Constants Refactoring Documentation
+
+## Overview
+This document describes the refactoring of #defines and common constants into a single centralized header file for Kyle's Editor (ke).
+
+## Changes Made
+
+### 1. Created `ke_constants.h`
+A new header file was created to centralize all common constants and preprocessor definitions used throughout the project.
+
+**Location**: `/Users/kyle/src/ke2/ke_constants.h`
+
+**Contents**:
+- **Version Information**: `KE_VERSION` - Editor version string
+- **Terminal Sequences**: `ESCSEQ` - ANSI escape sequence prefix
+- **Keyboard Macros**: `CTRL_KEY(key)` - Control key combination macro
+- **Display Constants**: 
+  - `TAB_STOP` (8) - Tab stop width
+  - `MSG_TIMEO` (3) - Message timeout in seconds
+- **Memory Management**: `INITIAL_CAPACITY` (64) - Initial buffer capacity
+- **Keyboard Modes**:
+  - `MODE_NORMAL` (0) - Normal editing mode
+  - `MODE_KCOMMAND` (1) - Command mode (^k commands)
+  - `MODE_ESCAPE` (2) - Escape key handling mode
+- **Kill Ring Operations**:
+  - `KILLRING_NO_OP` (0) - No operation
+  - `KILLRING_APPEND` (1) - Append deleted characters
+  - `KILLRING_PREPEND` (2) - Prepend deleted characters
+  - `KILLING_SET` (3) - Set killring to deleted character
+  - `KILLRING_FLUSH` (4) - Clear the killring
+- **Legacy Initializers**: `ABUF_INIT` - C struct initializer for append buffer
+
+### 2. Updated `main.c`
+- Added `#include "ke_constants.h"` at the top with other includes
+- Removed all duplicate #define statements that were moved to the constants header
+- Eliminated the duplicate `TAB_STOP` definition (was defined twice on lines 36 and 50)
+- Cleaned up approximately 30+ lines of redundant definitions
+
+### 3. Updated `erow.cpp`
+- Added `#include "ke_constants.h"` with extern "C" linkage for C++ compatibility
+- Removed local `constexpr int TAB_STOP = 8` definition
+- Now uses the centralized `TAB_STOP` constant from `ke_constants.h`
+
+## Benefits
+
+1. **Single Source of Truth**: All constants are now defined in one location, making them easier to maintain and modify
+2. **Eliminated Duplication**: Removed duplicate definitions (e.g., TAB_STOP was defined twice in main.c)
+3. **Better Organization**: Constants are grouped logically by category with clear comments
+4. **Cross-Language Compatibility**: Header works with both C (main.c) and C++ (erow.cpp) code
+5. **Easier Maintenance**: Future changes to constants only need to be made in one place
+6. **Improved Readability**: Cleaner source files with less clutter from #define statements
+
+## Build System Compatibility
+
+Both build systems have been tested and verified to work correctly:
+
+### Makefile Build
+```bash
+make clean
+make
+```
+Successfully compiles all files (main.c, abuf.cpp, erow.cpp) and links the executable.
+
+### CMake Build
+```bash
+cd cmake-build-debug
+cmake --build . --clean-first
+```
+Successfully builds the project with all components.
+
+## Header Guard
+The header uses standard include guards:
+```c
+#ifndef KE_CONSTANTS_H
+#define KE_CONSTANTS_H
+...
+#endif /* KE_CONSTANTS_H */
+```
+
+## C/C++ Interoperability
+When including in C++ files, use extern "C" linkage:
+```cpp
+extern "C" {
+#include "ke_constants.h"
+}
+```
+
+This ensures proper linkage and prevents name mangling issues.
+
+## Future Considerations
+
+1. **Additional Constants**: As the project grows, any new constants should be added to `ke_constants.h` rather than being scattered across source files
+2. **Namespacing**: For C++ constants, consider creating a dedicated C++ header with namespaced constants
+3. **Type Safety**: For C++ code, consider using `constexpr` or `inline constexpr` variables in a C++ header for better type safety
+4. **Documentation**: Keep this document updated as new constants are added or modified
+
+## Testing
+
+All compilation tests passed:
+- ✅ Makefile build: Clean compilation with no errors or warnings
+- ✅ CMake build: Clean compilation with no errors or warnings
+- ✅ All source files (C and C++) successfully include and use the constants
+- ✅ No duplicate definition errors
+- ✅ Proper linkage between C and C++ components
+
+## Related Files
+
+- `ke_constants.h` - The new constants header (created)
+- `main.c` - Updated to use new header (modified)
+- `erow.cpp` - Updated to use new header (modified)
+- `Makefile` - No changes required (working)
+- `CMakeLists.txt` - No changes required (working)
+
+## Date
+November 24, 2025