Assigning an object with implicit operator (cast to string) to Blazor component's parameter causes InvalidCastException

[Oblomoff]

Object

namespace BlazorBug
{
    public class Tag
    {
        public Tag(string value) => Value = value;

        public string Value { get; }

        /*
         * BUG!
         * 
         * This implicit operator causes InvalidCastException:
         * Unable to cast object of type 'System.String' to type 'BlazorBug.Tag'.
         * 
         * Comment the code below to avoid the exception.
         */
        public static implicit operator string(Tag tag) => tag.Value;
    }
}

Component

<h3>Tag Editor</h3>

<p>@Tag</p>

@code {
    [Parameter]
    public Tag Tag { get; set; }
}

Assignment

@page "/"

<TagEditor Tag="Tag" />

@code {
    public Tag Tag { get; } = new Tag("My Tag");
}

Exception

InvalidCastException: Unable to cast object of type 'System.String'
to type 'BlazorBug.Tag'.

InvalidOperationException: Unable to set property 'Tag' on object of type
'BlazorBug.Shared.TagEditor'. The error was: Unable to cast object of type
'System.String' to type 'BlazorBug.Tag'.

Sample project

BlazorBug.zip

This issue just killed our localization framework... Any updates on this one?

[GordonRudman]

I just came across this bug, which is preventing me from binding non-primitive objects (like Value Objects) to components that are designed to only accept those types of objects.
I see that this bug is about 2 years old already, so is it on any road map to get fixed in the near future?

[kieronlanning]

I've just wasted a morning tracking this down, any movement... updates? ...anything?

[delasource]

I came across by another way. I was assigning a string value to a Parameter, which is a reference type (like Tag in example above). The compiler says it's fine, but it breaks when running it, since "SetParametersAsync" works internally with reflection.

public static implicit operator Tag(string? value) => new() { Value = value };

Microsoft.AspNetCore.Components.Server.Circuits.RemoteRenderer: [12:30:33.8354]WARN ::RemoteRenderer.HandleException: Unhandled exception rendering component: Unable to set property 'Tag' on object of type 'TagComponent'. The error was: Unable to cast object of type 'System.String' to type 'Tag'. System.InvalidOperationException: Unable to set property 'Tag' on object of type 'TagComponent'. The error was: Unable to cast object of type 'System.String' to type 'Tag'.
 ---> System.InvalidCastException: Unable to cast object of type 'System.String' to type 'Tag'.
   at Microsoft.AspNetCore.Components.Reflection.PropertySetter.CallPropertySetter[TTarget,TValue](Action`2 setter, Object target, Object value)
   at Microsoft.AspNetCore.Components.Reflection.ComponentProperties.<SetProperties>g__SetProperty|2_0(Object target, PropertySetter writer, String parameterName, Object value)
   --- End of inner exception stack trace ---
   at Microsoft.AspNetCore.Components.Reflection.ComponentProperties.<SetProperties>g__SetProperty|2_0(Object target, PropertySetter writer, String parameterName, Object value)
   at Microsoft.AspNetCore.Components.Reflection.ComponentProperties.SetProperties(ParameterView& parameters, Object target)
   at Microsoft.AspNetCore.Components.ParameterView.SetParameterProperties(Object target)
   at Microsoft.AspNetCore.Components.ComponentBase.SetParametersAsync(ParameterView parameters)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.SetDirectParameters(ParameterView parameters)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewComponentFrame(DiffContext& diffContext, Int32 frameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewSubtree(DiffContext& diffContext, Int32 frameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InsertNewFrame(DiffContext& diffContext, Int32 newFrameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForRange(DiffContext& diffContext, Int32 oldStartIndex, Int32 oldEndIndexExcl, Int32 newStartIndex, Int32 newEndIndexExcl)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.ComputeDiff(Renderer renderer, RenderBatchBuilder batchBuilder, Int32 componentId, ArrayRange`1 oldTree, ArrayRange`1 newTree)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()

it seems like it ignores implicit operators at all.

[rmihael]

I also stumbled on it. I had something similar to the original problem, but with feature flags instead of tags.
Exception trace is not very helpful, so I spent more time on it than expected.

[glenn-kallidus]

Any update on this?