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Version: v2.0

Custom Mappers and Policy Composition

Use custom mappers when built-in failure mappings are not enough for your API contract.

Add Custom Failure Mappings​

using UnambitiousFx.Functional.AspNetCore;
using UnambitiousFx.Functional.AspNetCore.Mappers;

builder.Services.AddResultHttp(options =>
{
    options.AddMapper<RateLimitFailure>(429);

    options.AddMapper<PaymentRequiredFailure>(failure => new FailureHttpResponse
    {
        StatusCode = 402,
        Body = new { message = failure.Message }
    });
});

Configure Policy Defaults​

Global behavior can be tuned with adapter policy options, for example:

  • Non-generic Result success status (200 vs 204)
  • Maybe.None handling (404 vs 204)

Composition Guidelines​

  • Keep domain failures transport-agnostic.
  • Map transport semantics in one place (startup/composition root).
  • Prefer typed failures over message parsing for deterministic mapping.

See Also​