Forcing named arguments in C#

Question

C# 4 introduced a feature called named arguments which is especially useful in scenarios like

int RegisterUser(string nameFirst, string nameLast, string nameMiddle, string email) 

Is there a way to force using named arguments? Maybe some attribute to apply to a method or a compiler switch I'm not aware of? I guess it can be done with code inspector tools but just want to know if there is other way.

p.s.

For those interested why one may need it and why not just use a class/struct to utilize object initializers there are scenarios when it's impossible. Like calls to libraries not in your control or weird code conventions you have to obey.

Answer 1

It's possible to force the callers to always use named args. I wouldn't do this in most circumstances because it's rather ugly, but it depends on how badly safe method usage is needed.

Here is the solution:

    int RegisterUser( #if DEBUG       int _ = 0, #endif       string nameFirst = null,       string nameLast = null,       string nameMiddle = null,       string email = null) { /*...*/ } 

The first parameter is a dummy that shouldn't be used (and is compiled away in Release for efficiency). However, it ensures that all following parameters have to be named.

Valid usage is any combination of the named parameters:

    RegisterUser();     RegisterUser(nameFirst: "Joe");     RegisterUser(nameFirst: "Joe", nameLast: "Smith");     RegisterUser(email: "[email protected]"); 

When attempting to use positional parameters, the code won't compile.

Answer 2

No, not in the C# language. It will always accept positional parameters if all the parameters are supplied.

You could build a custom FxCop rule or an StyleCop rule to enforce this - as pointed out in the comments, it is likely a StyleCop rule you would be interested in (thanks to Kris).