# Welcome to arrow

Your guide to understanding the codebase

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### Learning Path

15 units • 5 levels

### Orchestration & APIs

- Pipelines, workflows, public interfaces • 3 units
- Apache Arrow Columnar Format and Type System
- Architecture·7
- Error Handling and Utility Functions
- Error Handling·2
- Memory Management and Array Builders
- Infrastructure·3

### Core Logic & Data

- Business rules, schemas, models • 3 units
- Data Serialization and IPC
- API·6
- File Formats and I/O
- Data Model·9
- Compute Kernels and SIMD Optimizations
- Workflow·18

### Interaction & Integration

- UI components, external connectors • 3 units
- Arrow Flight RPC and Flight SQL
- API·7
- Extension Types and Advanced Features
- Patterns·2
- Acero Query Engine and Dataset API
- Workflow·9

### Cross-Cutting Concerns

- Auth, logging, config, testing • 2 units
- Build Systems, Testing, and CI/CD
- Tooling·7
- Gandiva Expression Compiler and GPU Integration
- Workflow·9
- Edge Cases & Resilience
- Error handling, fault tolerance • 1 units

### Additional Data Model Patterns

- Data Model·9

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## Test Your Knowledge

Test your deep understanding of the codebase

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### Hands-On Assignment

2-3 hours

#### Your Challenge

Implement a custom extension type for storing geographic coordinates (latitude/longitude pairs) with validation in Apache Arrow. Your extension type should store coordinates as a FixedSizeList of two doubles, validate that latitude is between -90 and 90 and longitude is between -180 and 180, and provide serialization support so the type can be transmitted via IPC. This will require understanding Arrow's type system, array builders, and extension type registration mechanism.

### Starting Points

- `c_glib/arrow-cuda-glib/cuda.cpp:1-105`
  Examine how C++ Arrow types are wrapped in the GLib bindings, particularly the pattern of creating wrapper classes and handling memory management.

- `c_glib/arrow-cuda-glib/arrow-cuda-glib.h:1-27`
  Study the header structure and include patterns used for exposing Arrow functionality through GLib.

- `c_glib/test/file-system-tests.rb:1-134`
  Review the testing patterns used in the codebase - you'll need similar tests for your extension type.

### Success Criteria

- Extension type correctly stores coordinate pairs as FixedSizeList<double>[2]
- Builder validates latitude range [-90, 90] and longitude range [-180, 180], returning appropriate errors for invalid values
- Type can be serialized to IPC format and deserialized while preserving metadata
- At least 5 unit tests covering valid data, invalid data, serialization, and integration with Arrow arrays
- Type can be registered globally and retrieved by name
- Documentation comments explain the coordinate system and validation rules.

### Hints

- **Hint 1:** Understanding Extension Types conceptual
- **Hint 2:** Array Builder Pattern code location
- **Hint 3:** Registration and Serialization implementation
- **Hint 4:** Testing Your Implementation implementation

### Prerequisites

- C++ classes and inheritance
- Arrow type system basics
- Memory management with shared_ptr
- Basic understanding of coordinate systems

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### arrow - Learning Path