What are the drawbacks of using object as a return type in an ASP.NET controller action?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I’m using an ASP.NET controller action that returns a DTO wrapped in a generic result class containing a boolean status and a message, instead of a status code result.

This object is serialized, then de-serialized and cast into the appropriate type on the client side, so I assume boxing/unboxing isn’t an issue. However, are there any downsides to using object as the return type in such cases?

CSHARP
[Authorize(Policy = "Everyone")]
[HttpGet("testDto")]
public async Task<object> GetDTO([FromBody]string name)
{
    var dto = new TestDTO {
        Number = 123,
        Name = name,
        Data = new List<string>() { "aaa", "bbb", "ccc" }
    };

    var result = _resultFact.Result<TestDTO>(dto, true, "* result mesage *");

    return result;
}

Postman:

Comments 0

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Answers 3

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3 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

Using object as the return type can work, especially if you rely on a serialization framework that “unwraps” the object and the client then reinterprets the result. However, there are some downsides to consider:

Loss of Strong Typing

When you use object, you lose the compile‑time guarantees that come with a strongly typed API. This can make the code less self‑documenting and increase the risk of runtime errors (for example, if the client or subsequent code expects a particular shape). A more specific return type (or using something like ActionResult in ASP.NET Core) makes it clear what the API returns.

Potential Boxing Overhead

If your result contains value types, they will be boxed. Although boxing may not always be a performance bottleneck (especially when the overhead is dominated by serialization), it’s still an extra cost compared to returning a strongly typed value that avoids boxing.

Tooling and Refactoring

When the method returns a specific type, IDEs and refactoring tools can offer better support (intellisense, type checking, etc.). Returning object makes it harder for tools to infer the model, increasing the chance of mistakes during refactoring or maintenance.

Routing and Content Negotiation

ASP.NET Core can use return type metadata for content negotiation and producing appropriate HTTP responses. Returning object may obscure the actual type being returned, which can sometimes affect the extensibility of response formatting or error handling.

Summary

While there is no inherent “bug” in returning object if your serialization/deserialization strategy is robust, the trade-offs include reduced clarity and type safety, potential (even if minor) performance overhead from boxing, and less support from tooling. For these reasons, it’s usually preferable to return a more explicit type that best represents your response.

By considering these points, you can decide based on your project requirements and priorities.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by MartianPilot052 • 1 month ago

I have implemented multiple API endpoints with single object in return.

As per my knowledge, I do not see any downside except the list of objects. If the list of objects is large, then response time would be more.

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Answer by SupernovaObserver941 • 1 month ago

that will work but you will have some potential issues that I'm listing above

Tools like Swagger rely on method signatures to generate API
documentation. Using object won't provide meaningful details about
the return type, making it harder for API consumers to understand
what to expect
If your DTO contains derived or polymorphic
types, serialization might become tricky. Without explicit type
handling, the serializer may encounter issues
Unit tests can become more cumbersome because you'll need to cast
the returned object to its actual type every time to verify its
value.

If you want to use a generic type user instead of object. I'm providing an example, it might be useful:

CSHARP
public record Result<T>  
{  
   public bool Success {get; init;}  
   public string? Message {get; init;}  
   public T Data {get; set;}  
}  
  
public async Task<ActionResult<Result<TestDTO>>> GetDTO([FromBody] string name)  
{  
    var dto = new TestDTO  
    {  
        Number = 123,  
        Name = name,  
        Data = new List<string> { "aaa", "bbb", "ccc" }  
    };  
  
    var result = new Result<TestDTO>  
    {  
        Data = dto,  
        Status = true,  
        Message = "* result message *"  
    };  
  
    return Ok(result);  
}

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Discussion

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What are the drawbacks of using object as a return type in an ASP.NET controller action?

3 Answers

Loss of Strong Typing

Potential Boxing Overhead

Tooling and Refactoring

Routing and Content Negotiation

Summary

Discussion

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