Things I Learnt The Hard Way - Don't Use Booleans As Parameters

When you're designing a function, you may be tempted to add a flag (a parameter in a function that it is a boolean). Don't do this.

Here, let me show you an example: Suppose you have a messaging system and you have a function that returns all the messages to an user, called getUserMessages. But there is a case where you need to return a summary of each message (say, the first paragraph) or the full message. So you add a flag/Boolean parameter called retrieveFullMessage.

Again, don't do that.

'Cause anyone reading your code will see getUserMessage(userId, true) and wonder what the heck that true means.

You can either rename the function to getUserMessageSummaries and have another getUserMessagesFull or something around those lines, but each function just call the original getUserMessage with true or false -- but the interface to the outside of your class/module will still be clear.

But don't add flags/Boolean parameters to your API.