X39 – User talk

From Bohemia Interactive Community
Jump to navigation Jump to search
No edit summary
m (Blanking)
Tag: Blanking
 
(66 intermediate revisions by 3 users not shown)
Line 1: Line 1:
__TOC__
<code style="display: inline; margin: 0px; padding: 2px;">Status Quo Function</code> is the successor of <code style="display: inline; margin: 0px; padding: 2px;">[[SQS_syntax|Status Quo Script]]</code> which is deprecated since [[Armed Assault]].


== Language Structure ==
The SQF Language is fairly simple in how it is built.
In fact: there are barely any actual language structures at all.
The functionality is provided via so called ''operators'' (or more commonly known [[Category:Scripting_Commands_Arma_3|scripting commands]]).
Those operators are one of the following types: Nular, Unary or Binary.
=== Nular Operators ===
A Nular Operator is more or less a computed variable. Each time accessed, it will return the current state of something.
It is tempting to think of a Nular Operator as nothing more but a magic [[Variables|Global Variable]], but it is important to differentiate!
Consider following example in a mission with eg. 5 units:
{{codecomment|//Put the result of [[allUnits]] into a [[Variables|variable]].}}
_unitsArray = [[allUnits]];
{{codecomment|//Display the current array size using [[systemChat]].}}
[[systemChat]] [[str]] [[count]] _unitsArray;
{{codecomment|//Create a new unit in the player group.}}
[[group]] [[player]] [[createUnit]] ["B_RangeMaster_F", [[position]] [[player]], [], 0, "FORM"];
{{codecomment|//Output the array size again}}
[[systemChat]] [[str]] [[count]] _unitsArray;
{{codecomment|//Output the size of [[allUnits]]}}
[[systemChat]] [[str]] [[count]] [[allUnits]];
Now, what would the output of this look like?
System: 5
System: 5
System: 6
As you can see, <code style="display: inline; margin: 0px; padding: 2px;">_unitsArray</code> was not automatically updated. If [[allUnits]] was a [[Variables|Global Variable]], our private variable should have had reflected the change.
The reason for this is because [[allUnits]] and other Nular commands just return the current state of something and do not return a reference to eg. an [[Array]] containing all units.
It is generated each time, which is why some of theese commands are more expensive to run then ''just'' using a variable.
=== Unary Operators ===
The Unary Operators are operators that expect an argument on their right side (<code style="display: inline; margin: 0px; padding: 2px;">unary &lt;argument&gt;</code>). They always will take the first argument that occurs.
A common mistake would be the following:
{{codecomment|//Create some array containing three arrays.}}
_arr = [[1, 2, 3, 4, 5], [1, 2, 3, 4], [1, 2]];
{{codecomment|//Wrongly use the [[select]] command to get the count of the third array.}}
[[count]] _arr [[select]] 2; {{codecomment|//Error}}
Now, what went wrong?
Let's put some brackets in the right places to make the mistake understandible:
([[count]] _arr) [[select]] 2; {{codecomment|//Error}}
Due to the nature of Unary operators, count instantly consumes our [[Variables|variable]] ''_arr'' and returns the number ''3''.
The ''3'' then is passed to [[select]] which does not knows what to do with a number as left argument and thus errors out.
To do it correctly, one would have to put the <code style="display: inline; margin: 0px; padding: 2px;">_arr select 2</code> in brackets.
The correct code thus would be:
{{codecomment|//Create some array containing three arrays.}}
_arr = [[1, 2, 3, 4, 5], [1, 2, 3, 4], [1, 2]];
{{codecomment|//Use Brackets to correctly get count of the third array.}}
[[count]] (_arr [[select]] 2); {{codecomment|//Good :)}}
=== Binary Operators ===
Binary Operators expect two arguments (<code style="display: inline; margin: 0px; padding: 2px;">&lt;1st argument&gt; binary &lt;2nd argument&gt;</code>) and are executed according to their [[#precedence|precedence]]. If their [[#precedence|precedence]] is equal, they are executed left to right.
As example, we will look into the following Expression:
{{codecomment|//Create a nested [[Array]] with 5 levels.}}
_arr = [[[[[1]]]]];
{{codecomment|//Receive the nested number with some random math expressions.}}
_arr select 0 select 1 - 1 select 15 / 3 - 5 select 0 select 10 * 10 + 4 * 0 - 100
Now, let us analyze why this is happening for the first few expressions:
# _arr is loaded
# 0 is loaded
# [[select]] is executed with the result of 1. & 2.
# 1 is loaded
# 1 is loaded
# [a_minus_b|-] is executed with the result of 4. & 5.
# [[select]] is executed with the result of 3. & 6.
# ...
If we now would put brackets at the correct spots, the expression will get more clear:
((((_arr select 0) select (1 - 1)) select ((15 / 3) - 5)) select 0) select (((10 * 10) + (4 * 0)) - 100)
As you can see the [[a_*_b|*]] and [[a_/_b|/]] are executed first which matches their [[#precedence|precedence]]. Afterwards, the [[a_plus_b|+]] and [[a_minus_b|-]] operators will get executed followed by our [[select]] commands, which are executed from the left to the right.
== <span id="precedence">Rules Of Precedence</span> ==
{|
|1 '''Lowest Precedence'''
|<code>[[a or b|<nowiki>||</nowiki>]] [[a or b|or]]</code>
|-
|2
|<code>[[and|&&]] [[and]]</code>
|-
|3
|<code>[[==]] [[!=]] [[a_greater_b|&gt;]] [[a_less_b|&lt;]] [[a_less=_b|&gt;=]] [[a_less=_b|&lt;=]] [[config_greater_greater_name|&gt;&gt;]]</code>
|-
|4
|''ALL BINARY OPERATORS''
|-
|5
|<code>[[else]]</code>
|-
|6
|<code>[[a_plus_b|+]] [[a_minus_b|-]] [[max]] [[min]]</code>
|-
|7
|<code>[[a_*_b|*]] [[a_/_b|/]] [[mod|%]] [[mod]] [[atan2]]</code>
|-
|8
|<code>[[a_^_b|^]]</code>
|-
|9
|''ALL UNARY OPERATORS''
|-
|10 '''Highest Precedence'''
|''ALL NULAR OPERATORS, VARIABLES, VALUES OR BRACED EXPRESSIONS''
|}
<!-- [[Category: Syntax]] [[Category:Scripting Topics]] -->

Latest revision as of 22:12, 18 November 2019

Retrieved from "https://community.bistudio.com/wiki?title=User_talk:X39&oldid=138731"