ARC0005: Value produced by Provide is not consumed by Handle

Rule

When a command declares a Provide() method, every value it produces must be consumed by a parameter of the command’s Handle() method. A produced value that no Handle parameter can receive is almost always a mistake.

Control values that short-circuit execution rather than feed Handle — ValidationResult, AuthorizationResult, and CommandResult — are exempt.

Severity

Warning

Example

Violation

using Cratis.Arc.Commands.ModelBound;

[Command]
public record ApproveLoan(ApplicantId Applicant)
{
    public CreditScore Provide(ICreditBureau bureau) => bureau.GetScore(Applicant);

    public void Handle()
    {
    }
}

Provide returns a CreditScore, but Handle has no parameter that can receive it.

Fix

using Cratis.Arc.Commands.ModelBound;

[Command]
public record ApproveLoan(ApplicantId Applicant)
{
    public CreditScore Provide(ICreditBureau bureau) => bureau.GetScore(Applicant);

    public LoanApproved Handle(CreditScore creditScore) => new(Applicant, creditScore);
}

See Provide data to a command handler for the full pattern.