Keyed dictionaries

A keyed dictionary hands you every keyed implementation of a service, mapped by its key. It is the milk fridge as a whole. Ask for the fridge and you can reach for oat, whole, or soy by name at runtime.

Resolve the map

Register the implementations with keys, then depend on IReadOnlyDictionary<string, TService>.

[Container]
[Singleton<OatMilk, IMilk>(Key = "Oat")]
[Singleton<WholeMilk, IMilk>(Key = "Whole")]
[Singleton<SoyMilk, IMilk>(Key = "Soy")]
public static partial class CoffeeShop;

public sealed class MilkFridge(IReadOnlyDictionary<string, IMilk> milks)
{
    public IMilk Get(string kind) => milks[kind];
}

You can also resolve it directly:

var milks = shop.Resolve<IReadOnlyDictionary<string, IMilk>>();
IMilk oat = milks["Oat"];

What goes in

The dictionary contains every keyed registration of the service, keyed by its Key. Unkeyed registrations are left out. Each member keeps its own lifetime. With no keyed registrations, you get an empty dictionary.

The key type: string or enum

Awaiten synthesizes the dictionary for a string key or an enum key. For an enum-keyed map, register every implementation under a constant of the same enum and depend on IReadOnlyDictionary<TEnum, TService>:

public enum MilkKind { Oat, Whole, Soy }

[Container]
[Singleton<OatMilk, IMilk>(Key = MilkKind.Oat)]
[Singleton<WholeMilk, IMilk>(Key = MilkKind.Whole)]
public static partial class CoffeeShop;

public sealed class MilkFridge(IReadOnlyDictionary<MilkKind, IMilk> milks);

The dictionary synthesizes only when every keyed registration of the service matches the requested key type. A key type that is neither string nor an enum, or one whose registrations mix key kinds, is a build error (AWT159) unless you register the dictionary yourself. A synthesized dictionary already resolves every key, so applying [FromKey] to it makes no sense and is an error (AWT160).

The async form

For async members, ask for Task<IReadOnlyDictionary<string, TService>>. It awaits every member and keeps the consumer synchronously resolvable. If all members are synchronous, you get a completed task.

Where to go next

• Keyed services to select a single keyed implementation.
• Collections for all unkeyed implementations.