Can anybody tell me why I only get one object in the accumulator?

[UMDev-Brian]

public sealed class SetupSteps : List<ISetupStep>;
var config = DI.Setup(nameof(Composition))
.Accumulate<ISetupStep, SetupSteps>(Lifetime.Transient)
.Bind<ISetupStep>().As(Lifetime.Transient).To<LoadConfigs>()
.Bind<ISetupStep>().As(Lifetime.Transient).To<CoreSetupStep>()
.Root<(ISetupStep step, SetupSteps steps)>("Root")

The objects in question:

public abstract class SetupStep : ISetupStep
{
   //protected Composition _composition;
    // public SetupStep(Composition composition)
    // {
    //     _composition = composition;
    // }

    public abstract bool IsComplete();
    public abstract Task<bool> RunAsync(Composition composition, INavigationService frame);
}

public sealed class CoreSetupStep : SetupStep
{
    //public CoreSetupStep(Composition composition) : base(composition) { }
    public override bool IsComplete()
    {
        return true;
    }

    public override async Task<bool> RunAsync(Composition composition, INavigationService frame)
    {
        //do core setup
        return true;
    }

}

public sealed class LoadConfigs : SetupStep
{
   // public LoadConfigs(Composition composition) : base(composition) { }
    
    public override bool IsComplete()
    {
        return false;
        // return _composition.Settings == null || _composition.Settings.DbConfig == null || _composition.Settings.SquareConfig == null ||
        //        _composition.Settings.AzureConfig == null;
    }

    public override Task<bool> RunAsync(Composition composition, INavigationService frame)
    {
        //_composition = composition;
        //do services setup
        FlourishSettingsProvider.Initialize(composition);//TODO: this could be async
        return Task.FromResult(IsComplete());
    }

}

[NikolayPianikov]

The accumulator contains one object, because in fact one object of ISetupStep type was created.
To embed two objects you can embed a collection as in the example below. Also you have an error in the line .Bind<ISetupStep>().As(Lifetime.Transient).To<CoreSetupStep>() you have overridden the binding .Bind<ISetupStep>().As(Lifetime.Transient).To<LoadConfigs>() with a new one, the generator warned about it. To add a new one it can be labelled with some tag, in the example below it is ‘abc’.

DI.Setup(nameof(Composition))
    .Accumulate<ISetupStep, SetupSteps>(Lifetime.Transient)
    .Bind<ISetupStep>().As(Lifetime.Transient).To<LoadConfigs>()
    .Bind<ISetupStep>("abc").As(Lifetime.Transient).To<CoreSetupStep>()
    .Root<(IReadOnlyCollection<ISetupStep> allSteps, SetupSteps steps)>("Root");

var composition = new Composition();
var root = composition.Root;
var steps = root.steps;

return 0;

internal sealed class SetupSteps : List<ISetupStep>;

internal interface ISetupStep;

internal interface INavigationService;
    
internal abstract class SetupStep : ISetupStep
{
    //protected Composition _composition;
    // public SetupStep(Composition composition)
    // {
    //     _composition = composition;
    // }

    public abstract bool IsComplete();
    
    public abstract Task<bool> RunAsync(Composition composition, INavigationService frame);
}

internal sealed class CoreSetupStep : SetupStep
{
    //public CoreSetupStep(Composition composition) : base(composition) { }
    public override bool IsComplete()
    {
        return true;
    }

    public override async Task<bool> RunAsync(Composition composition, INavigationService frame)
    {
        //do core setup
        return true;
    }
}

internal sealed class LoadConfigs : SetupStep
{
    // public LoadConfigs(Composition composition) : base(composition) { }

    public override bool IsComplete()
    {
        return false;
        // return _composition.Settings == null || _composition.Settings.DbConfig == null || _composition.Settings.SquareConfig == null ||
        //        _composition.Settings.AzureConfig == null;
    }

    public override Task<bool> RunAsync(Composition composition, INavigationService frame)
    {
        //_composition = composition;
        //do services setup
        return Task.FromResult(IsComplete());
    }
}

[UMDev-Brian]

Thanks for the explanation! That makes a lot of sense. I will make the relevant changes.