proper replace

src/SteroidsDI.Tests/Cases/FactoryTests.cs

@@ -21,6 +21,49 @@ public void Named_Binding_Should_Throw_On_Unknown_Lifetime()
 Use the 'Named'/'Default' overloads with explicit Lifetime or first register 'SteroidsDI.Tests.IBuilder' in the DI container.");
     }
 
+    [Test]
+    public void Named_Binding_Should_Allow_The_Same_Type_With_Different_Names()
+    {
+        var services = new ServiceCollection()
+            .AddTransient<IBuilder, Builder>()
+            .For<IBuilder>()
+                .Named<SpecialBuilder>("aaa")
+                .Named<SpecialBuilder>("bbb")
+                .Named<SpecialBuilder>("ccc")
+            .Services;
+        services.Count.ShouldBe(5);
+    }
+
+    [Test]
+    public void Default_Binding_Should_Allow_Redeclaration()
+    {
+        var services = new ServiceCollection()
+            .AddTransient<IBuilder, Builder>()
+            .For<IBuilder>()
+                .Default<SpecialBuilder>()
+                .Default<SpecialBuilder>()
+            .Services;
+        services.Count.ShouldBe(3);
+        var def = (NamedBinding)services.Last().ImplementationInstance!;
+        def.Name.ShouldBeNull();
+        def.ImplementationType.ShouldBe(typeof(SpecialBuilder));
+    }
+
+    [Test]
+    public void Default_Binding_Should_Allow_Replace()
+    {
+        var services = new ServiceCollection()
+            .AddTransient<IBuilder, Builder>()
+            .For<IBuilder>()
+                .Default<SpecialBuilder>()
+                .Default<SpecialBuilderOver9000Level>()
+            .Services;
+        services.Count.ShouldBe(4);
+        var def = (NamedBinding)services[2].ImplementationInstance!;
+        def.Name.ShouldBeNull();
+        def.ImplementationType.ShouldBe(typeof(SpecialBuilderOver9000Level));
+    }
+
     [Test]
     [TestCase(true)]
     [TestCase(false)]

src/SteroidsDI/Factory/BindingContext.cs

@@ -90,7 +90,18 @@ public BindingContext<TService> Default<TImplementation>(ServiceLifetime lifetim
         if (existing == null)
             Services.Add(new ServiceDescriptor(typeof(TImplementation), typeof(TImplementation), lifetime));
 
-        Services.AddSingleton(new NamedBinding(null, typeof(TService), typeof(TImplementation)));
+        var def = new NamedBinding(null, typeof(TService), typeof(TImplementation));
+        var descriptor = ServiceDescriptor.Singleton(def);
+        for (int i = 0; i < Services.Count; ++i)
+        {
+            if (Services[i].ImplementationInstance is NamedBinding named && named.Name is null && named.ServiceType == typeof(TService))
+            {
+                Services[i] = descriptor;
+                return this;
+            }
+        }
+
+        Services.Add(descriptor);
 
         return this;
     }

src/SteroidsDI/Factory/NamedBinding.cs

@@ -7,7 +7,7 @@ namespace SteroidsDI;
 /// type <see cref="ImplementationType" /> in the required context.
 /// </summary>
 [DebuggerDisplay("{Name}: {ServiceType.Name} -> {ImplementationType.Name}")]
-internal sealed class NamedBinding
+internal sealed record NamedBinding
 {
     public NamedBinding(object? name, Type serviceType, Type implementationType)
     {