Factory Class Generator

Generate a GoF-style factory class from an abstract base or interface using [FactoryClass] on the base and [FactoryClassKey] on concrete implementations.

Quick start

using PatternKit.Generators.Factories;

namespace Demo;

[FactoryClass(typeof(string), FactoryTypeName = "NotificationFactory")]
public interface INotification { }

[FactoryClassKey("email")]
public class Email : INotification { }

[FactoryClassKey("sms")]
public class Sms : INotification { }

Generated factory (sync):

public sealed partial class NotificationFactory
{
    public INotification Create(string key);
    public bool TryCreate(string key, out INotification result); // unless GenerateTryCreate = false
}

Async is generated when any product exposes public static CreateAsync() returning Task<TBase> or ValueTask<TBase>:

public ValueTask<INotification> CreateAsync(string key);
public ValueTask<(bool Success, INotification Result)> TryCreateAsync(string key);

Enum keys

Set GenerateEnumKeys = true to emit:

Nested enum Keys containing all registered keys (sanitized identifiers).
Overloads of Create/TryCreate/CreateAsync/TryCreateAsync that accept the enum.

Behavior

Base requirement — [FactoryClass] must decorate an interface or abstract class.
Product discovery — [FactoryClassKey] types must be concrete and implement/derive exactly one [FactoryClass] base.
Construction — Uses public parameterless ctor when present; otherwise looks for static CreateAsync() on the product. Async factories are awaited; sync products are wrapped in ValueTask.FromResult for async APIs.
Key handling — Keys must convert implicitly to KeyType. Duplicate keys per base are rejected.
Defaults — No default branch; unknown keys throw in Create and return false in TryCreate.

Diagnostics

Id	Message	Fix
PKCF001	`[FactoryClass]` must be interface or abstract class	Mark the base `interface` or `abstract class`.
PKCF002	`[FactoryClassKey]` type maps to multiple bases	Ensure each product implements only one `[FactoryClass]` base.
PKCF003	`[FactoryClassKey]` type must be concrete	Remove `abstract` and supply an accessible ctor.
PKCF004	Duplicate factory key	Remove duplicate keys per base type.
PKCF005	Invalid factory key value	Ensure the key literal converts implicitly to `KeyType`.
PKCF006	Missing accessible constructor	Add public parameterless ctor or `static CreateAsync()` returning `Task/ValueTask<TBase>`.

Tips