Best way to check for null parameters (Guard Clauses)

Question

For example, you usually don\'t want parameters in a constructor to be null, so it\'s very normal to see some thing like

if (someArg == null)
{
    throw new Arg         


        

Answer 1

In C# 8.0 and later, new helps are available. C# 8.0 introduces non-nullable reference types (a feature somewhat confusingly called "nullable reference types" in the docs). Prior to C# 8.0, all reference types could be set to null. But now with C# 8.0 and the 'nullable' project setting, we can say that reference types are by default non-nullable, and then make our variables and parameters nullable on a case-by-case basis.

So whereas at the moment, we recognize code like this:

public void MyFunction(int thisCannotBeNull, int? thisCouldBeNull)
{
    // no need for checking my thisCannotBeNull parameter for null here
}

If you set enable for your C# v8.0+ project, you can do things like this too:

public void MyFunction(MyClass thisCannotBeNull, MyClass? thisCouldBeNull)
{
    // static code analysis at compile time checks to see if thisCannotBeNull could be null
}

The null-checking is done at compile-time, using static code analysis. So if you've coded it in a way that means a null could turn up there, you'll get a compiler warning (which you can upgrade to an error if you want). So lots (but not all) of the situations where you need a run-time check for null parameters can be handled as a compile-time check based on your code.