Difference between revisions of "If"

Revision as of 00:28, 6 March 2007

•	condition	–	If this executes as true then branch is executed.
•	branch	–	Can be either a single statement, a block statement, or a null statement.

**Conditional Types**
Type	Condition
integer	True if it is not zero.
float	True if it is not zero.^[1]
string	True if its length is not zero.
key	True only if it is a valid key and not NULL_KEY.
vector	True if the vector is not ZERO_VECTOR.
rotation	True if the rotation is not ZERO_ROTATION.
list	True if the length is not zero. Note that correct behavior is only seen with Mono-compiled scripts; LSO-compiled scripts incorrectly resolve to false if the list is non-empty: BUG-230728

^ The OpenSim LSL compiler will not do this implicitly. You will need to use an explicit check.

If

@@ Line 7: / Line 7: @@
 |p1_name=condition|p1_desc=If this executes as true then '''branch''' is executed.
 |spec
-|caveats
+|caveats=Operators in LSL are NOT short circuited. For example:
+<pre>
+// A simple method to say if the method was called.
+integer test() {
+    llOwnerSay("Test method called!");
+    return TRUE;
+}
+default {
+    touch_start(integer total_number) {
+        if (FALSE && test()) { // If the test is short-circuit optimized then the test() method should never be called.
+            // Will never get here.
+        }
+    }
+}
+</pre>
+In a short-circuited language if the left-hand side of a logical AND (&&) is FALSE the right-hand side is never tested since the entire test would always return a FALSE output no matter what the value of the right-hand side. Since LSL is not short circuited, both the left and the right-hand sides are tested all the time.
+This can be simulated by using a nested if structure:
+<pre>
+default {
+    touch_start(integer total_number) {
+        if (FALSE) {
+            if (test()) {
+              // Will never get here.
+            }
+        }
+    }
+}
+</pre>
 |examples
 |helpers