Boolean

From TeamDeveloperWiki

This page covers Boolean datatype tips & tricks.

Contents 1 How are expressions evaluated 2 What is a boolean in TD ?

How are expressions evaluated

Team Developer uses these precedence rules to evaluate expressions:

• Evaluate expressions with AND, OR, and NOT from left to right.

   If bError OR bStop
   !
   ! bError will be evaluated first, then bStop

• Stop evaluating AND/OR as soon as the result is known.

   If bError OR bStop
   !
   ! When bError is TRUE, bStop will not be evaluated
   ! When bError is FALSE, bStop will be evaluated
   !
   If bError AND bStop
   !
   ! When bError is TRUE, bStop will be evaluated
   ! When bError is FALSE, bStop will not be evaluated

• Evaluate expressions in parentheses first.

What is a boolean in TD ?

Internally, the boolean datatype is the same as the Number datatype.
The only difference between a Number and a Boolean is purely visual in the outline.
This means that you can assign any value to a Boolean, use them as it were normal numbers.

So beware, the next piece of code shows strange effects can happen when you are not aware of this

   Set bValue = 5
   If bValue = TRUE
      ...
   Else
      ! It evaluates to FALSE here
   If bValue
      ! It evaluates to TRUE here
   Else
      ...

So the best way to evaluate booleans is never use the TRUE or FALSE keywords.

   If bValue
      ! when boolean has any (negative) value except FALSE, 0, NUMBER_Null
   Else
      ! when boolean is FALSE, 0 or NUMBER_Null