C# String Interpolation on <appSettings>

Question

I am liking the new Interpolation syntax of C#.

I want to store a dynamic string in my .config file under appSettings and apply interpolation on it. The expected value of interpolatedMessage is "Your User Name is SnowWhite"

It would be great if this is possible. This will help me to keep the key to be configurable to any combination. (e.g. "SnowWhite is your User Name", "User Name - SnowWhite")

 <appSettings>
    <add key="userNameKey" value="Your User Name is {userName}" />
  </appSettings>

Answer 1

String interpolation is a syntax sugar that compiles to string format It means it needs to know all the details at compile time. In your case you only know the strings in run time and thus you need to use string format:

<appSettings>
    <add key="userNameKey" value="Your User Name is {0}" />
</appSettings>

Code:

var message = string.Format(ConfigurationManager["userNameKey"], userName);