I want to edit this answer.

I meant: write a new class with method generator.  And inherit from it.

I assume that's a comment  to my answer?

If yes, here's the working code. Maybe I missed some changes in my answer. Because, again, I needed to do too much changes to run the code in the first place.

Okay.

Please note, that only legacy IF sets $TEST and it is also one line long. New IF {} (3 lines, with brackets) does not set a $TEST variable.

There is rarely a need to modify web application config in production.

How would you have done it? It's 35 lines of code in total, 25 if we remove persistence (because singleton does not actually has persistence, but OP seemed to need it).

> you could not implement singleton which will be working across jobs, only for this same process;

Storing something in %/PPG would not work across jobs too. Singleton is a single-thread anyway.

> to share instance to teh object you could emply %-named variable or process-private global.

Wrote another singleton using % variable. How would I do it with PPG (any global)?  When you set global to an OREF it actually sets a string: "int@class".  And you could not  convert it back to an OREF with $$$objIntToOref at a later date because the object would be already destroyed.

/// Another singleton
Class Utils.Singleton2 Extends %SystemBase
{

Property Content As %String;

/// Set a = ##class(Utils.Singleton2).Get()
ClassMethod Get() As Utils.Singleton2
{
    #Define Var %Var
    If '$Data($$$Var) || '$IsObject($$$Var) {
        Set Obj = ..%New()
        Set $$$Var = Obj
    } Else {
        Set Obj = $$$Var
    }
    Return Obj
}

/// Do ##class(Utils.Singleton2).Test()
ClassMethod Test()
{
    Set a = ##class(Utils.Singleton2).Get()
    Set a.Content = $Random(100)
    
    Set b = ##class(Utils.Singleton2).Get()
    Write b.Content
}

}

>$SYSTEM.Status.GetErrorText(sc)["Something"

Would not always work correctly in applications with users requesting content in several languages (for example web app). Why not use error codes?

If $SYSTEM.Status.GetErrorCodes(sc)[$$$GeneralError $$$ThrowStatus(sc)

I usually add my classes and system classes I often reference from my classes into the project, so they can be opened faster (without dialog).

Since project is a collection of classes (and other items, yes, but we're talking about classes here) the  flow would be something like that:

• Get project name
• Project name to class list
• Get unit tests for class list
• Run unit tests

I'm just saying that 3rd step can have more callers (alternative routes to 3rd step if you will), for example:

• Package to class list
• Wildcard expression to class list
• Namespace to class list

One approach would be to use %XML.DataSet to convert SQL results into XML:

Set result=##class(%XML.DataSet).%New()                                  
Do result.Prepare("SELECT TOP 3 ID, Name FROM Sample.Person")
Do result.Execute()                                                      1
Do result.WriteXML("root",,,,,1) 

Outputs:

<root>
<s:schema id="DefaultDataSet" xmlns="" attributeFormDefault="qualified" elementFormDefault="qualified" xmlns:s="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
  <s:element name="DefaultDataSet" msdata:IsDataSet="true">
    <s:complexType>
      <s:choice maxOccurs="unbounded">
        <s:element name="SQL">
          <s:complexType>
            <s:sequence>
              <s:element name="ID" type="s:long" minOccurs="0" />
              <s:element name="Name" type="s:string" minOccurs="0" />
            </s:sequence>
          </s:complexType>
        </s:element>
      </s:choice>
    </s:complexType>
    <s:unique name="Constraint1" msdata:PrimaryKey="true">
      <s:selector xpath=".//SQL" />
      <s:field xpath="ID" />
    </s:unique>
  </s:element>
</s:schema>
<diffgr:diffgram xmlns:msdata="urn:schemas-microsoft-com:xml-msdata" xmlns:diffgr="urn:schemas-microsoft-com:xml-diffgram-v1">
<DefaultDataSet xmlns="">
  <SQL diffgr:id="SQL1" msdata:rowOrder="0">
    <ID>96</ID>
    <Name>Adam,Wolfgang F.</Name>
  </SQL>
  <SQL diffgr:id="SQL2" msdata:rowOrder="1">
    <ID>188</ID>
    <Name>Adams,Phil H.</Name>
  </SQL>
  <SQL diffgr:id="SQL3" msdata:rowOrder="2">
    <ID>84</ID>
    <Name>Ahmed,Edward V.</Name>
  </SQL>
</DefaultDataSet>
</diffgr:diffgram>
</root>

There is also %SQL.Export.Mgr class, which does SQL export.

%XML.Reader and %SQL.Import.Mgr respectively.