C#•17mo ago

❔ Builder with generics

Is possible create a builder that have classes with different parameters? An example

public class CommandHandlerFactory
{
    private readonly ICommandHandler<CreateGoogleAccountCommand> _googleAccountCommandHandler;
    private readonly ICommandHandler<CreateYahooAccountCommand> _yahooAccountCommandHandler;

    public CommandHandlerFactory(ICommandHandler<CreateGoogleAccountCommand> googleAccountCommandHandler, ICommandHandler<CreateYahooAccountCommand> yahooAccountCommandHandler)
    {
        _googleAccountCommandHandler = googleAccountCommandHandler;
        _yahooAccountCommandHandler = yahooAccountCommandHandler;
    }

    public ICommandHandler<T> Build<T>(ProviderAvaiablesEnum providers) where T : ICommand
    {

        var builder = new Dictionary<ProviderAvaiablesEnum, ICommandHandler<T>>
        {
            { ProviderAvaiablesEnum.Google, _googleAccountCommandHandler },
            { ProviderAvaiablesEnum.Yahoo _yahooAccountCommandHandler },
        };
        return builder[providers];
    }
}

// Command Handler interface
public interface ICommandHandler<in T> where T : ICommand
{
    Task<CommandResult> Execute(T command, CancellationToken cancellationToken = default);
}

// Command interface
public interface ICommand
{
    public ProviderAvaiablesEnum ProviderAvaiables { get; set; }
}

// Yahoo interface
public class CreateYahooAccountCommand : ICommand
{
    public ProviderAvaiablesEnum ProviderAvaiables { get; set; } = ProviderAvaiablesEnum.Yahoo
    ....
}

public class CommandHandlerFactory
{
    private readonly ICommandHandler<CreateGoogleAccountCommand> _googleAccountCommandHandler;
    private readonly ICommandHandler<CreateYahooAccountCommand> _yahooAccountCommandHandler;

    public CommandHandlerFactory(ICommandHandler<CreateGoogleAccountCommand> googleAccountCommandHandler, ICommandHandler<CreateYahooAccountCommand> yahooAccountCommandHandler)
    {
        _googleAccountCommandHandler = googleAccountCommandHandler;
        _yahooAccountCommandHandler = yahooAccountCommandHandler;
    }

    public ICommandHandler<T> Build<T>(ProviderAvaiablesEnum providers) where T : ICommand
    {

        var builder = new Dictionary<ProviderAvaiablesEnum, ICommandHandler<T>>
        {
            { ProviderAvaiablesEnum.Google, _googleAccountCommandHandler },
            { ProviderAvaiablesEnum.Yahoo _yahooAccountCommandHandler },
        };
        return builder[providers];
    }
}

// Command Handler interface
public interface ICommandHandler<in T> where T : ICommand
{
    Task<CommandResult> Execute(T command, CancellationToken cancellationToken = default);
}

// Command interface
public interface ICommand
{
    public ProviderAvaiablesEnum ProviderAvaiables { get; set; }
}

// Yahoo interface
public class CreateYahooAccountCommand : ICommand
{
    public ProviderAvaiablesEnum ProviderAvaiables { get; set; } = ProviderAvaiablesEnum.Yahoo
    ....
}

Compiler error,

Argument type 'Account.Importer.Domain.Commands.Contracts.ICommandHandler<Account.Importer.Domain.Commands.Contracts.CreateGoogleAccountCommand>' is not assignable to parameter type 'Account.Importer.Domain.Commands.Contracts.ICommandHandler<T>'

7 Replies

phaseshift•17mo ago

Generally, yes, but not with your Build<T> method, because T could be more derived than CreateGoogleAccountCommand, in which case its not valid

rcnespoliOP•17mo ago

So in this case how can I deal with this?

Omnissiah•17mo ago

essentially you can't, you either make a hack or you use object and casting but effectively i see the in T 🤔 ah no it's for Execute

rcnespoliOP•17mo ago

Yeah, I think it's not good use object or something casting

Omnissiah•17mo ago

i know the problem (of contravariance) is builder would be of the type of the interface with the less derived type Execute(ICommand command) but you are assigning it an interface with a more derived type Execute(CreateYahooAccountCommand command) so it can't cast because it would expose ICommand parameter which really would be for example a CreateYahooAccountCommand since it being ICommand you could really pass anything that inherits from that, not just CreateYahooAccountCommand

rcnespoliOP•17mo ago

Yeah.. i changed the approach.. I appreciate your time, thank you

Accord•17mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Builder with generics