List (SortOrder function): Difference between revisions

From m204wiki
Jump to navigation Jump to search
m (1 revision)
 
(8 intermediate revisions by 3 users not shown)
Line 1: Line 1:
{{Template:SortOrder:List subtitle}}
{{Template:SortOrder:List subtitle}}


This shared function is a [[Object variables#Virtual Constructor methods|virtual constructor]], or factory method, for <var>SortOrders</var>.
This shared function is a [[Object variables#Virtual Constructor methods|virtual constructor]], or factory method, for <var>SortOrder</var> objects.
The <var>List</var>
The <var>List</var>
method invokes the creation of a new <var>SortOrder</var> instance, then populates that
method invokes the creation of a new <var>SortOrder</var> instance, then populates that
instance with items from an input list that are themselves <var>SortOrder</var> instances.
instance with items from an input list that are themselves <var>SortOrder</var> instances.
Designed for specifying multiple sort criteria, the <var>SortOrders</var> in the object that
Designed for specifying multiple sort criteria, the <var>SortOrder</var> objects in the object that
<var>List</var> returns are applied consecutively by the sorting method
<var>List</var> returns are applied consecutively by the sorting method
that uses the <var>SortOrder</var>.
that uses the <var>SortOrder</var>.
==Syntax==
==Syntax==
{{Template:SortOrder:List syntax}}
{{Template:SortOrder:List syntax}}
Line 14: Line 15:
<tr><th>%sortOrder</th>
<tr><th>%sortOrder</th>
<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 nowrap="true"><var>[%(SortOrder For <i>itemType<var>)]</var>
<tr><th nowrap="true"><var>[%(SortOrder For </var>itemType<var>)]</var>
<td>For a shared function, this optional specification of the class in parentheses [[Notation conventions for methods#Shared methods|denotes a virtual constructor]]. See [[#Usage notes|"Usage notes"]], below, for more information about invoking a <var>SortOrder</var> virtual constructor. </td></tr>
<td>This optional specification of the class in parentheses [[Notation conventions for methods#Shared methods|denotes a virtual constructor]]. See [[#Usage notes|"Usage notes"]], below, for more information about invoking a <var>SortOrder</var> virtual constructor. </td></tr>
<tr><th>sortOrderItems</th>
<tr><th>sortOrderItems</th>
<td>A comma-delimited set of <var>SortOrder</var> objects, which may be explicitly specified [[Ascending and Descending (SortOrder functions)|Ascending/Descending]] functions, <var>SortOrder</var> object variables, or another <var>SortOrder</var> <var>List</var> specification. These individual <var>SortOrders</var> are applied to the target collection items in the order they are specified in this argument.
<td>A comma-delimited set of <var>SortOrder</var> objects, which may be explicitly specified [[Ascending and Descending (SortOrder functions)|Ascending/Descending]] functions, <var>SortOrder</var> object variables, or another <var>SortOrder</var> <var>List</var> specification. These individual <var>SortOrder</var> objects are applied to the target collection items in the order they are specified in this argument.
<p>
<p>
If a <var>SortOrder</var> like <code>ascending(price)</code> is a single sort criterion, then the maximum number of sort criteria a <var>List</var> call may produce is seven. </p></td></tr>
If a <var>SortOrder</var> like <code>ascending(price)</code> is a single sort criterion, then the maximum number of sort criteria a <var>List</var> call may produce is seven. </p></td></tr>
Line 29: Line 30:
<p class="code">%sord = List(<i>sortOrderItems</i>)
<p class="code">%sord = List(<i>sortOrderItems</i>)


%sord = %(Sortorder for float):List(<i>sortOrderItems</i>)
%sord = %(Sortorder for <i>itemType</i>):List(<i>sortOrderItems</i>)


%sord = %sord:List(<i>sortOrderItems</i>)
%sord = %sord:List(<i>sortOrderItems</i>)
</p>
</p>
'''Note:'''
<p class="note">'''Note:'''
As shown in the second of these above, if you explicitly specify the
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]].
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]]. </p></li>
</ul>
</ul>


Line 47: Line 48:
</p>
</p>


Since the arguments to the <var>SortOrder</var> <var>List</var> method are also <var>SortOrders</var>, you could
Since the arguments to the <var>SortOrder</var> <var>List</var> method are also <var>SortOrder</var> objects, you could
also pass the <code>%myorder</code> variable in another <var>List</var> call.
also pass the <code>%myorder</code> variable in another <var>List</var> call.
The following <var>List</var> statement
The following <var>List</var> statement

Latest revision as of 16:04, 6 April 2015

Create a composite SortOrder (SortOrder class)


This shared function is a virtual constructor, or factory method, for SortOrder objects. The List method invokes the creation of a new SortOrder instance, then populates that instance with items from an input list that are themselves SortOrder instances. Designed for specifying multiple sort criteria, the SortOrder objects in the object that List returns are applied consecutively by the sorting method that uses the SortOrder.

Syntax

%sortOrder = [%(SortOrder For itemType):]List( sortOrderItems)

Syntax terms

%sortOrder A SortOrder object variable to contain the new object instance.
[%(SortOrder For itemType)] 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.
sortOrderItems A comma-delimited set of SortOrder objects, which may be explicitly specified Ascending/Descending functions, SortOrder object variables, or another SortOrder List specification. These individual SortOrder objects are applied to the target collection items in the order they are specified in this argument.

If a SortOrder like ascending(price) is a single sort criterion, then the maximum number of sort criteria a List call may produce is seven.

Usage notes

  • List is a virtual constructor and as such can be invoked with no method object, with an explicit class specification, or with an object variable of the class, even if that object is Null:

    %sord = List(sortOrderItems) %sord = %(Sortorder for itemType):List(sortOrderItems) %sord = %sord:List(sortOrderItems)

    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.

Examples

The typical way to use SortOrder lists is in a collection class sorting method invocation:

%orders:sort(%myorder)

Where, for example:

%myorder = list(ascending(quantity), descending(price))

Since the arguments to the SortOrder List method are also SortOrder objects, you could also pass the %myorder variable in another List call. The following List statement inserts the %myorder criteria into the middle of two other sort criteria:

%mynewOrder = list(ascending(length), %myorder, descending(reverse))

You can even pass a List call within a List call:

%myorder = list(ascending(change), list(ascending(quantity), descending (price)))

See also