ItemNotFound class: Difference between revisions

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__NOTOC__
__NOTOC__
An <var>ItemNotFound</var> exception indicates that a collection object search located no collection items that satisfy the selection criterion specified in the collection method that invoked the search.
An <var>ItemNotFound</var> exception indicates that a collection object search located no collection items that satisfy the selection criterion specified in the collection method that invoked the search.
There are several methods for [[Collections#Searching a collection|"searching a collection"]], but only those that return a single found item produce an <var>ItemNotFound</var> exception.
There are several [[Collections#Searching a collection|searching]] methods, but only those that return a single found item produce an <var>ItemNotFound</var> exception.
   
   
This exception class has no properties.  It is simply a notification that a valid search found no items that met the selection criterion.
This exception class has no properties.  It is simply a notification that a valid search found no items that met the selection criterion.
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The <var>Try/Catch</var> approach is slightly more efficient than a test for a zero result.  <var>[[Try]]</var> generates no quads other than the branch around the catch block if the search succeeds.  And in fact, you could put a <var>Try</var> around a loop and use the <var>ItemNotFound</var> exception to exit the loop:
The <var>Try/Catch</var> approach is slightly more efficient than a test for a zero result.  <var>[[Try]]</var> generates no quads other than the branch around the catch block if the search succeeds.  And in fact, you could put a <var>Try</var> around a loop and use the <var>ItemNotFound</var> exception to exit the loop:
<p class="code"> %i = 0
<p class="code"> %i = 0
  [[try]]
  try
     repeat forever
     repeat forever
       %i = %colla:findNextItemNumber(<criterion>), start=%i)
       %i = %colla:findNextItemNumber(<criterion>), start=%i)
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       ... process the object
       ... process the object
     end repeat
     end repeat
  [[catch]] itemNotFound
  catch itemNotFound
  end try
  end try
</p>
</p>
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<h2>Code property</h2>
<h2>New constructor</h2>
{{Template:ItemNotFound:New subtitle}}
This callable constructor generates an instance of an <var>[[ItemNotFound_class|ItemNotFound]]</var> exception. The <var>New</var> method format follows:
 
==Syntax==
{{Template:ItemNotFound:New syntax}}
===Syntax terms===
<table class="syntaxTable">
<tr><th>%itemNotFound</th>
<td>A reference to an instance of an <var>ItemNotFound</var> object.
</td></tr>
<tr><th><var>%(ItemNotFound)</var></th><td>The class name in parentheses denotes a shared method.</td></tr>
</table>
 


[[Category:System exception classes]]
[[Category:System exception classes]]

Revision as of 16:25, 10 May 2011


An ItemNotFound exception indicates that a collection object search located no collection items that satisfy the selection criterion specified in the collection method that invoked the search. There are several searching methods, but only those that return a single found item produce an ItemNotFound exception.

This exception class has no properties. It is simply a notification that a valid search found no items that met the selection criterion.

The class's only method is the New constructor, which you would typically use with a User Language Throw statement to produce an ItemNotFound exception. For example:

throw %(itemNotFound):new

When working with the collection searching methods, remember that an exception is thrown only if there is a catcher for the exception. For example, if you expect one or no matches from your search, you might specify a block like the following:

try %terminationInfo = - %terminationList:findNextItem (eq(custId, %custid) ... process the termination info catch itemNotFound end try

On the other hand, if you always expect a match, you might want a program crash to result if you are wrong about the match, so you could leave out a Try/Catch.

The Try/Catch approach is slightly more efficient than a test for a zero result. Try generates no quads other than the branch around the catch block if the search succeeds. And in fact, you could put a Try around a loop and use the ItemNotFound exception to exit the loop:

%i = 0 try repeat forever %i = %colla:findNextItemNumber(<criterion>), start=%i) %obj = %colla(%i) ... process the object end repeat catch itemNotFound end try

The ItemNotFound class is available as of version 7.6.


The ItemNotFound methods

The following are the available ItemNotFound class methods.

MethodDescription
NewCreate a new ItemNotFound object

The methods in the class are described in the subsections that follow. In addition:


New constructor

Create a new ItemNotFound object (ItemNotFound class) This callable constructor generates an instance of an ItemNotFound exception. The New method format follows:

Syntax

%itemNotFound = [%(ItemNotFound):]New

Syntax terms

%itemNotFound A reference to an instance of an ItemNotFound object.
%(ItemNotFound)The class name in parentheses denotes a shared method.