# Learning Path

## Welcome to arrow

Your guide to understanding the codebase.

## Overview

15 units • 5 levels

## 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 unit
- Additional Data Model Patterns (Data Model·9)

## Test Your Knowledge

### Progress
0/26 answered

### Question Tiers
- **Why**: 8
- **Purpose & Problem**: Architecture 10
- **Design & Patterns**: Code 8
- **Implementation**: 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