c# - Conditional operator assignment with Nullable<value> types?

Question

EmployeeNumber =
string.IsNullOrEmpty(employeeNumberTextBox.Text)
    ? null
    : Convert.ToInt32(employeeNumberTextBox.Text),

I often find myself wanting to do things like this (EmployeeNumber is a Nullable<int> as it's a property on a LINQ-to-SQL dbml object where the column allows NULL values). Unfortunately, the compiler feels that

There is no implicit conversion between 'null' and 'int'

even though both types would be valid in an assignment operation to a nullable int on their own.

Using the null coalescing operator is not an option as far as I can see because of the inline conversion that needs to happen on the .Text string if it's not null.

As far as I know the only way to do this is to use an if statement and/or assign it in two steps. In this particular case I find that very frustrating because I wanted to use the object initializer syntax and this assignment would be in the initialization block...

Does anyone know a more elegant solution?

Answer 1

The problem occurs because the conditional operator doesn't look at how the value is used (assigned in this case) to determine the type of the expression -- just the true/false values. In this case, you have a null and an Int32, and the type can not be determined (there are real reasons it can't just assume Nullable<Int32>).

If you really want to use it in this way, you must cast one of the values to Nullable<Int32> yourself, so C# can resolve the type:

EmployeeNumber =
    string.IsNullOrEmpty(employeeNumberTextBox.Text)
    ? (int?)null
    : Convert.ToInt32(employeeNumberTextBox.Text),

or

EmployeeNumber =
    string.IsNullOrEmpty(employeeNumberTextBox.Text)
    ? null
    : (int?)Convert.ToInt32(employeeNumberTextBox.Text),