Simpler checking of arguments with C# 7 throw expressions

C# 7 has made a simple and important change to C# throw statements. They are now expressions.

So what does that mean for you? It means that now you can check your arguments with a simpler statement.

One such recurring pattern is in the constructor of a class, where you get passed some mandatory dependency. This dependency cannot be null, and then needs to be stored. If the dependency is null, you want to throw an ArgumentNullException.

Here is an example in C# 6

if( context != null )
{
  throw new ArgumentNullException(nameof(context));
}
this.context = context;

Compare this with the C# 7 version:

this.context = context ?? throw new ArgumentNullException(nameof(context));

We assign the context field a value with the null-coalescing operator which takes the left side if it is null (and doesn't evaluate the right side). If the left side is null, it evaluates the right side, which throws an ArgumentNullException.

Way simpler and elegant!