Strange behavior with ChildLifetimeScope, IEnumerable and Singleton.

[Akeit0]

First, I prepared these classes.

public class A
{
    static int instanceCount = 0;
    readonly int instanceId = instanceCount++;
    public override string ToString()
    {
        return $"A {instanceId}";
    }
}
public class BaseLifetimeScope : LifetimeScope
{
    protected override void Configure(IContainerBuilder builder)
    {
        builder.Register<A>(Lifetime.Singleton).AsSelf();
        builder.RegisterBuildCallback(x =>
        {
               Debug.Log("BaseLifetimeScope "+x.Resolve<A>());
        });
    }
}
public class ChildLifetimeScope : LifetimeScope
{
    protected override void Configure(IContainerBuilder builder)
    {
        builder.RegisterBuildCallback(resolver =>
        {
            Debug.Log("ChildLifetimeScope "+string.Join(",", resolver.Resolve<IEnumerable<A>>()));
        });
    }
}

Log

BaseLifetimeScope A 0
ChildLifetimeScope A 0

This seems fine.

But, when I changed the ChildLifetimeScope as follows

public class ChildLifetimeScope : LifetimeScope
{
    protected override void Configure(IContainerBuilder builder)
    {
        builder.Register<A>(Lifetime.Singleton).AsSelf();// I changed this part.
        
        builder.RegisterBuildCallback(resolver =>
        {
            Debug.Log("ChildLifetimeScope "+string.Join(",", resolver.Resolve<IEnumerable<A>>()));
        });
    }
}

logs changed to

BaseLifetimeScope A 0
ChildLifetimeScope A 1,A 2

.
I assumed It would be like ChildLifetimeScope A 1,A 0.

I don't know what the intended behavior is, but I don't think the result is intended.

[hadashiA]

Thanks for the report. it is strange..

📝
Internally, the key of the ConcurrentDictionary holding the Singleton is Registration, but when multiple registrations are found in the parent and child, the keys don't match, so it looks like they are duplicate instantiated.

[hadashiA]

Fixed in #698 .

Now the behavior is as follows.

• If a Singleton of the same type is registered for each Parent/Child, each container can have an instance. (This has been the specification for some time.)
• In this case, when Child resolves IEnumerable, it searches for an instance of each Parent/Child. That is, the number of elements will be 2
  • If Singleton already exists in Parent, it is used.