If
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if ( condition ) branch
• | condition | – | If this executes as true then branch is executed. | |
• | branch | – | Can be either a single statement, a block statement, or a null statement. |
|
if ( condition ) branch_true else branch_false
• | condition | – | If this executes as true then branch is executed. | |
• | branch_true | – | Can be either a single statement, a block statement, or a null statement. | |
• | branch_false | – | Can be either a single statement, a block statement, or a null statement. |
Specification
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 |
Examples
Simple inline if statement:
if (a == 1) c = b;
Simple block if statement:
if (a == 1) { // Do something here. }
Compounded if statement:
if (a == 1 && b == c) { // more here. }
Nested if statements:
if (a == 1) { if (b == c) { // more here. } }
Notes
Watch out for misplaced semicolons. They can, and will, cause strange things to happen. For instance: If you place a semicolon between an if statement and a code block, the if statement will not control the execution of the block.
if (a == "Loren"); { llSay(0, "Lorem ipsum sic amet!"); } |
This code will execute in the following order:
|
Another problem happens when someone forgets to use the curly braces.
if (a == "Loren") llSay(0, "Lorem ipsum sic amet!"); llSay(0, "I don't know what it means either...");
The assumption is that because the indentation makes it "look" like both llSay commands are controlled by the if statement, that they are. In fact, if a
was equal to "Joe" then all that would be said is "I don't know what it means either..."
Operators in LSL are NOT short circuited. For example:
// 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. } } }
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:
default { touch_start(integer total_number) { if (FALSE) { if (test()) { // Will never get here. } } } }
Deep Notes
Footnotes
- ^ The OpenSim LSL compiler will not do this implicitly. You will need to use an explicit check.