Ascending and Descending (SortOrder functions): Difference between revisions

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These shared methods create a new instance of the <var>SortOrder</var> class.
These shared methods create a new instance of the <var>SortOrder</var> class.
The ordering direction of the new instance is given by the constructor name:
The ordering direction of the new instance is given by the method name:
<var>Ascending</var> is low-to-high; <var>Descending</var> is high-to-low.
<var>Ascending</var> is low-to-high; <var>Descending</var> is high-to-low.


The sorting key of the new instance is specified by the input parameter
The sorting key of the new instance is specified by the input parameter
to the constructor.
to the method.
This parameter is a function that gets
This parameter is a function that gets
applied to each item in the collection that is being sorted, and it must be
applied to each item in the collection that is being sorted, and it must be
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<td>A <var>SortOrder</var> object variable to contain the new object instance. </td></tr>
<td>A <var>SortOrder</var> object variable to contain the new object instance. </td></tr>
<tr><th><var>%(SortOrder For</var> itemtype)</th>
<tr><th><var>%(SortOrder For</var> itemtype)</th>
<td>This optional specification of the class in parentheses indicates that the method is [[Notation conventions for methods#Shared methods|shared]] and does not operate on a specific instance. If you use this option, however, you must include the collection item type to which the selection expression will be applied, like this: <code>%(SortOrder For <i>itemtype</i>):</code> </td></tr>
<td>For a shared function, this optional specification of the class in parentheses denotes a [[Notation conventions for methods#Shared methods|virtual constructor]]. See [[#Usage notes|"Usage notes"]], below, for more information about invoking a <var>SortOrder</var> virtual constructor.  </td></tr>
<tr><th>itemFunction</th>
<tr><th>itemFunction</th>
<td>A method value (a method name literal, a method variable, a class <var>Variable</var>,
<td>A method value (a method name literal, a method variable, a class <var>Variable</var>, or even a method that returns a method value) for a method that operates on objects of the type specified on the declaration of the collection being sorted, and that returns a numeric or string value.  
or even a method that returns a method value) for a method
<p>
that operates on objects of the type specified on the
The default <var class="term">itemFunction</var> value as of <var class="product">Sirius Mods</var> version 7.6 is the special value <var>This</var>, described further in the "Usage Notes," below. </p></td></tr>
declaration of the collection being sorted, and that returns a numeric or
string value.  
<br>
The default <var class="term">itemFunction</var> value as of <var class="product">Sirius Mods</var> version 7.6 is the special value <var>This</var>, described further in the "Usage Notes," below. </td></tr>
</table>
</table>


==Usage Notes==
==Usage Notes==
<ul>
<ul>
<li>For more information about the <var class="term">itemFunction</var> parameter,
see [[SortOrder class#Specifying a SortOrder's sort key method|"Specifying a SortOrder's sort key method"]].
<li><var>Ascending</var> and <var>Descending</var> are virtual constructors and as such can be called with
<li><var>Ascending</var> and <var>Descending</var> are virtual constructors and as such can be called with
no method object, with an explicit class specification, or with an object variable of the class,
no method object, with an explicit class specification, or with an object variable of the class,
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%sortOrder = %sortOrder:Descending(<i>itemFunction</i>)
%sortOrder = %sortOrder:Descending(<i>itemFunction</i>)
</p>
</p>
<li>The parameter in the <var>Ascending</var> and <var>Descending</var> methods is a method value, not a <var class="product">User Language</var> expression,
'''Note:'''
As shown in the second of these above, if you explicitly specify the
class name, you must include the item datatype of the collection to be sorted, just as on a <var>SortOrder</var> object variable's [[SortOrder class#Declaring a SortOrder object variable|declaration]].
<li>For more information about the <var class="term">itemFunction</var> parameter,
see [[SortOrder class#Specifying a SortOrder's sort key method|"Specifying a SortOrder's sort key method"]].
The parameter is a method value, not a <var class="product">User Language</var> expression,
and you may not specify a function that itself has an argument.
and you may not specify a function that itself has an argument.
In order to do this, see the [[SortOrder class#xmplocal|example using a Local function]], which shows a way to apply such a function in a sort.
In order to do this, see the [[SortOrder class#xmplocal|example using a Local function]], which shows a way to apply such a function in a sort.

Revision as of 19:30, 1 August 2011

Create SortOrder object to sort in ascending or descending order (SortOrder class)


These shared methods create a new instance of the SortOrder class. The ordering direction of the new instance is given by the method name: Ascending is low-to-high; Descending is high-to-low.

The sorting key of the new instance is specified by the input parameter to the method. This parameter is a function that gets applied to each item in the collection that is being sorted, and it must be a method that operates on the item type and returns a User Language intrinsic datatype (Float, String, Longstring, or Unicode) value.

Ascending/Descending syntax

%sortOrder = [%(SortOrder For itemType):]Ascending[( [itemFunction])]

%sortOrder = [%(SortOrder For itemType):]Descending[( [itemFunction])]

Syntax terms

%sortOrder A SortOrder object variable to contain the new object instance.
%(SortOrder For itemtype) For a shared function, this optional specification of the class in parentheses denotes a virtual constructor. See "Usage notes", below, for more information about invoking a SortOrder virtual constructor.
itemFunction A method value (a method name literal, a method variable, a class Variable, or even a method that returns a method value) for a method that operates on objects of the type specified on the declaration of the collection being sorted, and that returns a numeric or string value.

The default itemFunction value as of Sirius Mods version 7.6 is the special value This, described further in the "Usage Notes," below.

Usage Notes

  • Ascending and Descending are virtual constructors and as such can be called with no method object, with an explicit class specification, or with an object variable of the class, even if that object is Null:

    %sortOrder = Descending(itemFunction) %sortOrder = %(SortOrder for float):Descending(itemFunction) %sortOrder = %sortOrder:Descending(itemFunction)

    Note: As shown in the second of these above, if you explicitly specify the class name, you must include the item datatype of the collection to be sorted, just as on a SortOrder object variable's declaration.

  • For more information about the itemFunction parameter, see "Specifying a SortOrder's sort key method". The parameter is a method value, not a User Language expression, and you may not specify a function that itself has an argument. In order to do this, see the example using a Local function, which shows a way to apply such a function in a sort.
  • As of Sirius Mods version 7.6, the default SortOrder itemFunction value is This, a method value that is valid for User Language intrinsic method objects only. The identity method This returns the value of the method object to which it is applied. The following statements are therefore equivalent:

    %sortOrder = Descending(this) %sortOrder = Descending

    Note: Using the default SortOrder above on a non-intrinsic method object produces a compilation error.

See also

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