ItemNotFound class: Difference between revisions
m (tags and edits) |
mNo edit summary |
||
| Line 1: | Line 1: | ||
<!-- ItemNotFound class --> | <!-- ItemNotFound class --> | ||
__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 methods for [[Collections#Searching a collection|"searching a collection"]], but only those that return a single found item produce an <var>ItemNotFound</var> exception. | ||
| Line 31: | Line 32: | ||
</p> | </p> | ||
The methods in | The <var>ItemNotFound</var> class is available as of <var class="product">[[Category:System exception classes]]</var> version 7.6. | ||
<h2>The ItemNotFound methods</h2> | |||
{{Template:List of ItemNotFound methods}} | |||
The methods in the class are described in the subsections that follow. In addition: | |||
<ul> | |||
<li>[[Notation conventions for methods|"Notation conventions for methods"]] has information | |||
about the conventions followed. | |||
<li>[[ItemNotFound methods syntax|"ItemNotFound methods syntax"]] is a single page that contains the syntax diagrams of all the methods in the class. | |||
</ul> | |||
<h2>Code property</h2> | |||
[[Category:System exception classes]] | [[Category:System exception classes]] | ||
Revision as of 16:12, 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 methods for "searching a collection", 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.
| Method | Description |
|---|---|
| New | Create a new ItemNotFound object |
The methods in the class are described in the subsections that follow. In addition:
- "Notation conventions for methods" has information about the conventions followed.
- "ItemNotFound methods syntax" is a single page that contains the syntax diagrams of all the methods in the class.