OliveStudio.MissingAttributes

A C# library providing compiler polyfills for modern language features in .NET Framework and .NET Standard. This library enables you to use the latest C# language features like records, init properties, and required members in projects targeting older frameworks.

Installation

# Package manager
Install-Package OliveStudio.MissingAttributes

# .NET CLI
dotnet add package OliveStudio.MissingAttributes

What are Compiler Polyfills?

Compiler polyfills are types that enable newer C# language features to work with older .NET runtime versions like .NET Framework. The C# compiler looks for specific types and attributes to enable language features. By providing these types, you can use the latest C# syntax even when targeting .NET Framework or .NET Standard.

Included Polyfills

`IsExternalInit`

Enables the init accessor for properties, allowing you to create immutable objects and records.

Enables:

init property setters
Records with init properties
Object initializers with init properties

// Without polyfill: Only works in .NET 5+
// With polyfill: Works in .NET Standard 2.0+

public class Person
{
    public string Name { get; init; }
    public int Age { get; init; }
}

// Usage
var person = new Person 
{ 
    Name = "John Doe", 
    Age = 30 
};

// person.Name = "Jane"; // Compile error - init properties are read-only after initialization

`RequiredMemberAttribute`

Enables the required modifier for properties and fields, ensuring they must be initialized during object creation.

Enables:

Required properties and fields
Compile-time enforcement of initialization
Better API design with mandatory parameters

// Without polyfill: Only works in .NET 7+
// With polyfill: Works in .NET Standard 2.0+

public class User
{
    public required string Name { get; init; }
    public required string Email { get; init; }
    public string? PhoneNumber { get; init; } // Optional
}

// Usage
var user = new User
{
    Name = "John Doe",    // Required - compiler error if missing
    Email = "[email protected]" // Required - compiler error if missing
    // PhoneNumber is optional
};

// var invalid = new User { Name = "John" }; // Compile error - Email is required

`SetsRequiredMembersAttribute`

Indicates that a constructor sets all required members, allowing object creation without object initializers.

Enables:

Constructors that satisfy required member constraints
Clean APIs that don't force object initializer syntax
Better encapsulation with constructor-based initialization

public class User
{
    public required string Name { get; init; }
    public required string Email { get; init; }
    public string? PhoneNumber { get; init; }

    // This constructor sets all required members
    [SetsRequiredMembers]
    public User(string name, string email)
    {
        Name = name;
        Email = email;
    }
    
    // Parameterless constructor still requires object initializer
    public User() { }
}

// Usage - both are valid:
var user1 = new User("John Doe", "[email protected]"); // Constructor sets required members
var user2 = new User { Name = "Jane", Email = "[email protected]" }; // Object initializer

`CompilerFeatureRequiredAttribute`

Indicates that compiler support for specific features is required. This attribute helps with advanced scenarios and compiler feature detection.

Properties:

FeatureName: The name of the required compiler feature
IsOptional: Whether the compiler can allow access if it doesn't understand the feature

Built-in Feature Names:

RefStructs: For ref struct types
RequiredMembers: For required members feature

// Example usage (advanced scenarios)
[CompilerFeatureRequired(CompilerFeatureRequiredAttribute.RefStructs)]
public ref struct MyRefStruct
{
    public int Value;
}

[CompilerFeatureRequired(CompilerFeatureRequiredAttribute.RequiredMembers)]
public class MyClass
{
    public required string Name { get; init; }
}

Usage Examples

Records (Enabled by IsExternalInit)

// Simple record
public record User(string Name, string Email);

// Record with additional properties
public record Product
{
    public string Name { get; init; }
    public decimal Price { get; init; }
    public string Category { get; init; }
    
    public Product(string name, decimal price)
    {
        Name = name;
        Price = price;
    }
}

// Usage
var user = new User("Alice", "[email protected]");
var product = new Product("Laptop", 999.99m) { Category = "Electronics" };

// Records provide value equality
var user2 = new User("Alice", "[email protected]");
Console.WriteLine(user == user2); // True

// Records support with expressions for immutable updates
var updatedUser = user with { Email = "[email protected]" };

Init-Only Properties

public class Configuration
{
    public string ConnectionString { get; init; }
    public int TimeoutSeconds { get; init; } = 30;
    public bool EnableLogging { get; init; } = true;
}

// Usage
var config = new Configuration
{
    ConnectionString = "Server=localhost;Database=MyDb",
    TimeoutSeconds = 60,
    EnableLogging = false
};

// config.ConnectionString = "new value"; // Compile error

Immutable Collections

public class GameState
{
    public IReadOnlyList<Player> Players { get; init; } = Array.Empty<Player>();
    public string CurrentLevel { get; init; }
    public int Score { get; init; }
    public DateTime StartTime { get; init; } = DateTime.UtcNow;
}

// Usage
var gameState = new GameState
{
    Players = new[] { new Player("Alice"), new Player("Bob") },
    CurrentLevel = "Level 1",
    Score = 0
};

// Create new state (immutable update pattern)
var newGameState = gameState with 
{ 
    Score = gameState.Score + 100,
    CurrentLevel = "Level 2"
};

Required Members with Constructors

public class DatabaseConnection
{
    public required string ConnectionString { get; init; }
    public required string Database { get; init; }
    public int TimeoutSeconds { get; init; } = 30;
    
    // Constructor that sets required members
    [SetsRequiredMembers]
    public DatabaseConnection(string connectionString, string database)
    {
        ConnectionString = connectionString;
        Database = database;
    }
    
    // Parameterless constructor for frameworks/serializers
    public DatabaseConnection() { }
}

// Both approaches work:
var conn1 = new DatabaseConnection("Server=localhost", "MyApp");
var conn2 = new DatabaseConnection 
{ 
    ConnectionString = "Server=localhost", 
    Database = "MyApp",
    TimeoutSeconds = 60 
};

Required Members with Records

public record CreateUserRequest
{
    public required string Name { get; init; }
    public required string Email { get; init; }
    public int? Age { get; init; } // Optional
    public string? PhoneNumber { get; init; } // Optional
    
    // Constructor for cleaner API
    [SetsRequiredMembers]
    public CreateUserRequest(string name, string email)
    {
        Name = name;
        Email = email;
    }
    
    public CreateUserRequest() { } // For model binding
}

// Usage options:
var request1 = new CreateUserRequest("Alice Smith", "[email protected]");
var request2 = new CreateUserRequest
{
    Name = "Alice Smith",     // Required
    Email = "[email protected]", // Required
    Age = 25                  // Optional
};

API Models

public record CreateUserRequest
{
    public string Name { get; init; }
    public string Email { get; init; }
    public int? Age { get; init; }
}

public record UserResponse(
    int Id,
    string Name,
    string Email,
    DateTime CreatedAt);

// Controller usage
[HttpPost]
public async Task<UserResponse> CreateUser(CreateUserRequest request)
{
    // request properties are immutable after binding
    var user = await _userService.CreateAsync(request.Name, request.Email, request.Age);
    
    return new UserResponse(user.Id, user.Name, user.Email, user.CreatedAt);
}

Target Framework Support

This library enables the latest C# features in:

.NET Framework 4.6.1 and later
.NET Standard 2.0 and later
.NET Core 2.0 and later

Primary Focus: Bringing modern C# language features to .NET Framework projects that can't upgrade to newer .NET versions.

Features that become available:

C# 9.0: Records, init properties
C# 11.0: Required members

Project Configuration

Add this to your project file to use modern C# versions with older frameworks:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net48</TargetFramework> <!-- .NET Framework 4.8 -->
    <LangVersion>latest</LangVersion> <!-- Enable latest C# features -->
  </PropertyGroup>
  
  <PackageReference Include="OliveStudio.MissingAttributes" Version="1.0.0" />
</Project>

Migration Example

Before (Traditional Classes):

public class User
{
    public User(string name, string email)
    {
        Name = name ?? throw new ArgumentNullException(nameof(name));
        Email = email ?? throw new ArgumentNullException(nameof(email));
    }
    
    public string Name { get; }
    public string Email { get; }
    
    public override bool Equals(object obj) { /* boilerplate */ }
    public override int GetHashCode() { /* boilerplate */ }
    public override string ToString() { /* boilerplate */ }
}

After (With Polyfills):

public record User(string Name, string Email);

Benefits

Modern Syntax: Use latest C# features in .NET Framework projects
No Runtime Dependency: Works with existing .NET Framework applications
Backward Compatibility: Deploy to .NET Framework while using modern C# code
Reduced Boilerplate: Records eliminate equals, hash code, and toString implementations
Immutability: Init properties help create immutable objects
Team Productivity: Developers can use familiar modern C# syntax
Migration Path: Easier to upgrade projects incrementally

Best Practices

1. Use Records for Data Transfer Objects

// API models
public record LoginRequest(string Username, string Password);
public record LoginResponse(string Token, DateTime ExpiresAt);

// Domain events
public record UserCreatedEvent(int UserId, string Email, DateTime CreatedAt);

2. Use SetsRequiredMembers for Clean APIs

public class ApiConfiguration
{
    public required string BaseUrl { get; init; }
    public required string ApiKey { get; init; }
    public int TimeoutMs { get; init; } = 5000;
    
    [SetsRequiredMembers]
    public ApiConfiguration(string baseUrl, string apiKey)
    {
        BaseUrl = baseUrl;
        ApiKey = apiKey;
    }
    
    public ApiConfiguration() { } // For configuration binding
}

public class DatabaseOptions
{
    public string ConnectionString { get; init; }
    public int CommandTimeout { get; init; } = 30;
    public bool EnableRetry { get; init; } = true;
}

3. Prefer Init Properties for Configuration

public class DatabaseOptions
{
    public string ConnectionString { get; init; }
    public int CommandTimeout { get; init; } = 30;
    public bool EnableRetry { get; init; } = true;
}

4. Use With Expressions for Updates

public record UserSettings(string Theme, bool Notifications, string Language)
{
    public UserSettings WithTheme(string newTheme) => this with { Theme = newTheme };
    public UserSettings WithNotifications(bool enabled) => this with { Notifications = enabled };
}

Common Scenarios

Value Objects in Domain-Driven Design

public record Money(decimal Amount, string Currency)
{
    public Money Add(Money other)
    {
        if (Currency != other.Currency)
            throw new InvalidOperationException("Cannot add different currencies");
            
        return this with { Amount = Amount + other.Amount };
    }
}

Immutable Game State

public record GameState(
    int Level,
    int Score,
    TimeSpan TimeRemaining,
    IReadOnlyList<string> Inventory)
{
    public GameState AddScore(int points) => this with { Score = Score + points };
    public GameState NextLevel() => this with { Level = Level + 1, TimeRemaining = TimeSpan.FromMinutes(5) };
}

Name		Name	Last commit message	Last commit date
Latest commit History 7 Commits
OliveStudio.MissingAttributes		OliveStudio.MissingAttributes
.gitignore		.gitignore
OliveStudio.MissingAttributes.sln		OliveStudio.MissingAttributes.sln
README.md		README.md

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OliveStudio.MissingAttributes

Installation

What are Compiler Polyfills?

Included Polyfills

`IsExternalInit`

`RequiredMemberAttribute`

`SetsRequiredMembersAttribute`

`CompilerFeatureRequiredAttribute`

Usage Examples

Records (Enabled by IsExternalInit)

Init-Only Properties

Immutable Collections

Required Members with Constructors

Required Members with Records

API Models

Target Framework Support

Project Configuration

Migration Example

Benefits

Best Practices

1. Use Records for Data Transfer Objects

2. Use SetsRequiredMembers for Clean APIs

3. Prefer Init Properties for Configuration

4. Use With Expressions for Updates

Common Scenarios

Value Objects in Domain-Driven Design

Immutable Game State

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olivegamestudio/OliveStudio.MissingAttributes

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OliveStudio.MissingAttributes

Installation

What are Compiler Polyfills?

Included Polyfills

IsExternalInit

RequiredMemberAttribute

SetsRequiredMembersAttribute

CompilerFeatureRequiredAttribute

Usage Examples

Records (Enabled by IsExternalInit)

Init-Only Properties

Immutable Collections

Required Members with Constructors

Required Members with Records

API Models

Target Framework Support

Project Configuration

Migration Example

Benefits

Best Practices

1. Use Records for Data Transfer Objects

2. Use SetsRequiredMembers for Clean APIs

3. Prefer Init Properties for Configuration

4. Use With Expressions for Updates

Common Scenarios

Value Objects in Domain-Driven Design

Immutable Game State

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`IsExternalInit`

`RequiredMemberAttribute`

`SetsRequiredMembersAttribute`

`CompilerFeatureRequiredAttribute`

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