YENGtry

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(Created page with "try, catch and finally allow to handle some exceptions without getting the script killed. * on the try block we place the code we want to run protected. * on the catch block ...")
 
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try, catch and finally allow to handle some exceptions without getting the script killed.
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<div style="background-color:#FFA0A0; padding:10px; padding-bottom:5px; border: 1px #FF544F solid">
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'''There can not be any llResetScript, osResetAllScripts or llDie inside any of this blocks. script will compile but fail with a severe runtime error
 +
</div><br>
  
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* on the try block we place the code we want to run protected.
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try, catch and finally allow to handle some exceptions (see [[runtime exceptions]]) without getting the script killed.
−
* on the catch block or blocks we place code to handle the exceptions
+
−
* on the finally block we place code that should run always.
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a try block must be follow by at least one catch or finally block
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* On the try block we place the code we want to run protected.
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there can be several catch blocks one per exception type, but only one finally
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* On a catch blocks we place code to handle the exceptions
 +
* On the finally block we place code that should always run.
 +
* throw keyword allows a catch to reissue the exception, so the engine handles it normally
 +
 
 +
A try block must be follow by at least
 +
one or two of the following catch types (possible more in future),
 +
one finally block
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all of those
 +
 
 +
<div style="background-color:#FFA500; padding:10px; padding-bottom:5px; border: 1px #FF544F solid">
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'''at this time there are only 2 types of catch blocks
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to catch script related exceptions
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 +
catch(scriptexception ex) { }
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to catch any available exception a script can intercept:
 +
 
 +
catch(exception ex) { }
 +
 
 +
in both cases particular exception must be found by looking to the message.<br>
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The catch blocks types are checked by their order in source.<br>
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Only the first that matches the exception type is executed, so if both needed scriptexception should be first.<br>
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</div><br>
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There are a few auxiliary functions.
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 +
= string yExceptionMessage(exception ex) =
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returns a string with the message of the exception ex
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= string yExceptionTypeName(exception ex) =
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 +
returns a string with system name of the exception. scriptexception will return ScriptException
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so catch(scriptexception ex) could be
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 +
<source lang="lsl">
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catch(exception ex)
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{
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    if(yExceptionTypeName(ex) == "ScriptException")
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    {
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        ...
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    }
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}
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</source >
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but catch(scriptexception ex) is faster and more readable
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 +
= Examples =
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Make sure to add yoptions; to the second line of the script, usually line number 1 starting from 0.
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Silly example.
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<source lang="lsl">
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touch_start(integer nn)
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{
 +
    integer a = 0;
 +
 
 +
    try
 +
    {
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        llSay(PUBLIC_CHANNEL,"try");       
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        float c = 1 / a;
 +
    }
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    catch(scriptexception ex)
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    {
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        if(yExceptionMessage(ex) == "Division by Zero")
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            llSay(PUBLIC_CHANNEL,"Where did you learn math?");
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        else
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            throw;
 +
    }
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    finally
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    {
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        llSay(PUBLIC_CHANNEL,"finaly");
 +
    }
 +
}
 +
</source >
 +
 
 +
Detect no ossl permission.
 +
 
 +
<source lang="lsl">
 +
touch_start(integer n)
 +
{
 +
    try
 +
    {
 +
        key agent = llDetectedKey(0);
 +
        osForceOtherSit(agent);
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    }
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    catch(scriptexception ex)
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    {
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        string message = yExceptionMessage(ex);
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        if(osStringStartsWith(message,"ossl permission error", TRUE))
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            llSay(PUBLIC_CHANNEL, "You need to enable  osForceOtherSit on osslEenable.ini");
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        else
 +
            throw;
 +
    }
 +
}
 +
</source >
 +
 
 +
[[Category:Scripts]]

Latest revision as of 19:15, 12 October 2022

There can not be any llResetScript, osResetAllScripts or llDie inside any of this blocks. script will compile but fail with a severe runtime error


try, catch and finally allow to handle some exceptions (see runtime exceptions) without getting the script killed.

  • On the try block we place the code we want to run protected.
  • On a catch blocks we place code to handle the exceptions
  • On the finally block we place code that should always run.
  • throw keyword allows a catch to reissue the exception, so the engine handles it normally

A try block must be follow by at least 

one or two of the following catch types (possible more in future),
one finally block
all of those

at this time there are only 2 types of catch blocks

to catch script related exceptions

catch(scriptexception ex) { }

to catch any available exception a script can intercept:

catch(exception ex) { }

in both cases particular exception must be found by looking to the message.
The catch blocks types are checked by their order in source.
Only the first that matches the exception type is executed, so if both needed scriptexception should be first.


There are a few auxiliary functions.

[edit] string yExceptionMessage(exception ex)

returns a string with the message of the exception ex

[edit] string yExceptionTypeName(exception ex)

returns a string with system name of the exception. scriptexception will return ScriptException

so catch(scriptexception ex) could be 

catch(exception ex)
{
    if(yExceptionTypeName(ex) == "ScriptException")
    {
        ...
    }
}

but catch(scriptexception ex) is faster and more readable

[edit] Examples 

Make sure to add yoptions; to the second line of the script, usually line number 1 starting from 0.

Silly example. 

touch_start(integer nn)
{
    integer a = 0;
 
    try
    {
        llSay(PUBLIC_CHANNEL,"try");        
        float c = 1 / a;
    }
    catch(scriptexception ex)
    {
        if(yExceptionMessage(ex) == "Division by Zero")
            llSay(PUBLIC_CHANNEL,"Where did you learn math?");
        else
            throw;
    }
    finally
    {
        llSay(PUBLIC_CHANNEL,"finaly");
    }
}

Detect no ossl permission. 

touch_start(integer n)
{
    try
    {
        key agent = llDetectedKey(0);
        osForceOtherSit(agent);
    }
    catch(scriptexception ex)
    {
        string message = yExceptionMessage(ex);
        if(osStringStartsWith(message,"ossl permission error", TRUE))
            llSay(PUBLIC_CHANNEL, "You need to enable  osForceOtherSit on osslEenable.ini");
        else
            throw;
    }
}
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