.NET & C# Language Cheatsheet

Purpose

The primary language for developing applications on the .NET platform, designed for productivity, performance, and robustness.

Core Characteristics

• Object-Oriented: Supports encapsulation, inheritance, and polymorphism.
• Type-Safe: Prevents type errors that could lead to insecure or unstable code.
• Component-Oriented: Based on software components with properties, methods, and events.
• Unified Type System: All C# types inherit from a single root `object` type.
• Garbage Collection: Automatic memory management simplifies development.
• Evolving Language: Regularly updated with new features to enhance productivity and capabilities (e.g., .NET 8 / C# 12). What's New in C# 12

Purpose

Manages I/O-bound and CPU-bound asynchronous operations without complex callback structures, improving application performance and responsiveness.

Key Concepts

• `async` Modifier: Marks a method as asynchronous.
• `await` Operator: Suspends execution until an awaited `Task` or `Task` completes.
• `Task` and `Task`: Represent ongoing asynchronous operations.
• Exception Handling: `try-catch` blocks work seamlessly with async operations.

Use Cases

Web service calls, database queries, file I/O, long-running computations that shouldn't block the main thread.

Purpose

Offers a consistent model for working with data across various sources and formats, reducing complexity and improving code readability.

Key Features

• Query Syntax & Method Syntax: Two ways to write LINQ queries.
• Standard Query Operators: A rich set of methods like `Where`, `Select`, `OrderBy`, `GroupBy`.
• Deferred Execution: Queries are executed only when results are enumerated.
• Type Safety: Queries are checked at compile time.
• Providers: LINQ to Objects, LINQ to Entities (EF Core), LINQ to XML, etc.

Purpose

Provides more concise and readable syntax for conditional logic based on data characteristics, type checks, and value comparisons.

Types of Patterns

• Type Pattern: Checks if an expression can be converted to a specified type (`obj is string s`).
• Property Pattern: Matches an expression against properties of an object (`obj is { Length: > 0 }`).
• Relational Patterns: Compare values (`> 10`, `< 50`).
• Logical Patterns: Combine patterns (`and`, `or`, `not`).
• List Patterns: Match elements in arrays or lists (`[1, 2, ..]`). (C# 11+)
• Switch Expressions: Concise switch-like construct returning a value.

Purpose

Simplify the creation of data-centric types, promote immutability, and provide built-in functionality for value-based equality and display.

Key Features

• Immutability by Default: Properties are typically init-only.
• Value-based Equality: Instances are compared based on their data, not reference.
• `with` Expressions: Create copies with modified properties (non-destructive mutation).
• Built-in Formatting: Sensible `ToString()` overrides.
• Deconstruction: Easily extract property values.
• Positional Records: Concise syntax for defining properties via constructor parameters.

Purpose

Improves code safety by making the intent regarding nullability explicit, allowing the compiler to issue warnings about potential null dereferences.

Mechanism

• Opt-in Feature: Enabled via project settings (`enable`) or `#nullable` directives.
• `string?` vs `string`: `string?` indicates a reference type that can be null; `string` indicates it should not be null.
• Compiler Warnings: Alerts for potential null assignments or dereferences.
• Null-Forgiving Operator (`!`): Suppresses warnings when a developer asserts an expression is not null.

Impact

Encourages more robust code by forcing developers to consider nullability throughout their codebase.