C# 10: Constant Interpolated Strings

Prior to C# 10, you couldn’t use string interpolation (`$”…”`) in `const` declarations. Now you can, as long as all parts are also constants.

Example

const string BasePath = "/api";
const string Version = "v1";
const string Endpoint = $"{BasePath}/{Version}/users"; // Now valid!

Use Case

Useful for defining attribute strings cleanly.

[Route($"{ApiRoutes.Users}")]
public class UsersController : ControllerBase { }

Key Takeaways

• Components must be `const`; no runtime expressions allowed.
• Good for reducing magic strings.