While investigating a routine bug fix today, I came across some code that can only be described as a buried cry for help …

public void Adjust(
    DateTime? open, DateTime? due, DateTime? close)
    if (!open.HasValue)
        throw new ArgumentNullException("open");
    if (!due.HasValue)
        throw new ArgumentNullException("due");
    if (!close.HasValue)
        throw new ArgumentNullException("close");
    // ...

Why would a developer declare parameters as nullable DateTimes and then immediately write guard clauses to prevent nulls from being accepted.

If you don’t want to support nulls, use a regular date time.

There are two lessons to learn here, one specific and one general.

The specific lesson: Use the right type for each parameter - use the most liberal type that makes sense (for example, use IEnumerable<T> instead of IList<T> unless you need indexed access), but no more liberal (don’t use DateTime? unless you’re willing to accept nulls).

The general lesson: Don’t make code more complex than it needs to be - do things the simplest way that makes sense. Being a developer is hard enough, we shouldn’t go out of our way to make it harder.


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