Following on from last week’s introduction of the plus operator, a friend of mine challenged me to consider an alternative operator for combining validation results:
After a bit of experimentation, I managed to get it going - and supporting
&& adds some interesting capabilities that are very useful.
In C#, you can’t override the
&& operator directly; you instead need to separately implement three operators.
The first is
& - and the implementation exactly parallels the implementation we showed last week for
The other two operators we need to implement are true and false - and we need to decide what it means for a
ValidationResult to be truthful.
I suggest that we want true to indicate that we’re able to proceed with using whatever it is that we’ve just validated. Put another way, we want false to mean that we have at least one error, and shouldn’t use the item.
The implementations are straightforward:
&& operator does short-circuiting - if the left-hand expression is false, the right hand one isn’t evaluated at all.
Using this, we can now write elegant validation code like this:
If no value is supplied for
UserName, the error returned by
UserNameIsMandatory means that nothing further happens. We only incur the cost of checking against the database if we have a
UserName to check.
Since we’ve implemented true and false as operators, we can now use the value directly in if conditions:
I really like the way
&& works, especially the short circuiting … but I’m not really sure what I think of using
ValidationResult inside an if expression. What do you think? Weigh in with your thoughts, below.