Lambda Exercises in C#

A hands-on curriculum for mastering C# lambdas, delegates, LINQ, closures, async, and expression trees.
Each day introduces a focused set of exercises with unit tests to guide implementation.

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📂 Project Structure

lambda-exercises-csharp/ ├─ src/ # Library projects (Day01, Day02, …) ├─ tests/ # xUnit test projects ├─ lambda-exercises-csharp.sln └─ README.md

• src/DayXX_* → library with exercise stubs / implementations
• tests/DayXX_*.Tests → xUnit test projects driving the exercises

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🚀 Getting Started

1. Clone the repo

   git clone https://github.com/Vexmage/lambda-exercises-csharp.git
   cd lambda-exercises-csharp
   

Build and run tests

dotnet build dotnet test

Pick a day

Open the corresponding src/DayXX_* folder and work through the exercises. The unit tests in tests/DayXX_*.Tests will guide your progress.

📘 Curriculum

Day 1: Basics Map, Filter, Reduce, lambda syntax, closure capture pitfalls.

Day 2: Delegates & Closures Custom delegates, counters, partial application, memoization.

Day 3: LINQ Core Select, Where, Any/All, Aggregate, GroupBy.

Day 4: LINQ Advanced Joins, GroupJoin, DistinctBy, Lookups, paging.

Day 5: Extensions & Composition Pipe, Tee, WhereIf, Compose, predicate combinators.

Day 6: Events & Async Pipelines Event handlers, tasks, continuations, cancellation.

Day 7: Expressions & Performance Expression trees, dynamic query building, compiled delegates.

Definitions

Lambdas

Anonymous functions (inline pieces of code like x => x * 2) that can be passed around as values. They make code concise and expressive, especially for quick transformations or filters without needing to define a full method.

Delegates

Type-safe references to methods. A delegate defines a function signature (Func<T, U>, Action, or custom) that lambdas or methods must match. They enable flexible APIs where behavior is passed as a parameter (e.g., a Comparison for sorting).

LINQ (Language Integrated Query)

A set of features and APIs in .NET that use lambdas to query and transform collections (.Where, .Select, .GroupBy). It lets you write SQL-like logic directly in C#, making data manipulation expressive and readable.

Closures

When a lambda "captures" variables from the surrounding scope. Closures make it possible to preserve state across function calls (e.g., counters), but also introduce pitfalls if you accidentally capture changing loop variables.

Async

Short for asynchronous programming — writing methods (async Task) that run without blocking the main thread. Useful for I/O-bound work like file access, APIs, or database calls; lambdas often appear in async continuations (.ContinueWith(t => ...)) or async LINQ-style pipelines.

Expression Trees

Data structures that represent code (lambdas) as an object tree instead of compiled delegates. They’re powerful for building dynamic queries (e.g., Entity Framework translating a u => u.Age > 18 expression into SQL) or for meta-programming scenarios.

🛠 Tools & Frameworks

.NET 9 SDK xUnit for testing FluentAssertions for expressive assertions