api-reference-core.md

API Reference: Core Abstractions

This document covers the core contracts in the D20Tek.Vertically namespace. These are the types you implement when authoring a vertical slice: the request marker interfaces, the handler interfaces, the validator interfaces, and the optional self-registering feature contract.

See the API Reference hub for the other reference documents.

Table of Contents

• Request Interfaces
• Handler Interfaces
• Validator Interfaces
• Feature Interface

Request Interfaces

A request carries its result type so that handlers, behaviors, and registration can discover the request-to-result pairing from the request alone.

Interface	Type Parameters	Description
ICommand<TResult>	TResult : notnull	Marker for a command that, when handled, produces a result of type TResult. Use for operations that change state.
IQuery<TResult>	TResult : notnull	Marker for a query that, when handled, produces a result of type TResult. Use for read operations.

Handler Interfaces

Handlers implement the logic for a single request and return a Result<TResult>. You inject the closed handler interface directly into presentation code and call HandleAsync.

Interface	Type Parameters	Member	Return Type	Description
ICommandHandler<TCommand, TResult>	TCommand : ICommand<TResult>, TResult : notnull	HandleAsync(TCommand command, CancellationToken ct)	Task<Result<TResult>>	Handles the specified command asynchronously and returns a Result wrapping the command result.
IQueryHandler<TQuery, TResult>	TQuery : IQuery<TResult>, TResult : notnull	HandleAsync(TQuery query, CancellationToken ct)	Task<Result<TResult>>	Handles the specified query asynchronously and returns a Result wrapping the query result.

Validator Interfaces

Validators run before the handler when the validation behavior is enabled. Implement the synchronous contract for in-memory checks and the asynchronous contract when validation requires I/O or remote calls.

Interface	Type Parameters	Member	Return Type	Description
IValidator<T>	T : notnull	Validate(T input)	ValidationErrors	Validates the input synchronously and returns any validation errors.
IAsyncValidator<T>	T : notnull	ValidateAsync(T input, CancellationToken ct)	Task<ValidationErrors>	Validates the input asynchronously and returns any validation errors.

Feature Interface

A feature bundles a slice's command or query, handler, validator, and any slice-specific service registrations into a single self-registering unit. Implementers are discovered during assembly scanning (before the loose handler scan), instantiated via their parameterless constructor, and asked to register themselves.

Interface	Member	Return Type	Description
IFeature	Register(IVerticallyBuilder builder)	void	Registers this feature's handlers, validators, behaviors, and services against the supplied builder. Because static classes cannot implement interfaces, a feature is a non-static class whose Command/Handler/Validator types may still be nested inside it. For AOT and trim safety, use explicit generic registration and avoid nested assembly scans.