Variable Names

The following are some general guidelines for variable names:

• Variable names should be between 8 - 20 characters long. Usually between 8-16 characters.
• Variable names should clearly communicate what the variable stores.
• Use mixed case for variable names.
• Avoid use of the _ underscore character in your variable names if possible. It makes them longer and more work to type.
• Use the suffix Ext to indicate a variable that instantiates an external object. (e.g. ioFileOpsExt or oFileOpsExt

Task Variables

Try to limit the use of task variables. In object-oriented programming you always use the lowest possible scope for each variable. I normally only use task variables to instantiate object classes which need application wide scope.

Task variables are all lower case and usually a shortened name of the object class they point to. The task variable names are misspelled on purpose so that Find & Replace can be used to find all occurrences of a specific task variable in the code.

The following are examples of startup task task variables:

• cn - points to the oConstants object class
• errhndlr - points to the oErrorHandler object class
• fn - points to the oFunctions object class
• pths - points to the oPaths object class

Shorter task variable names look cleaner in the code.

Do fn.$retAlphaNumeric(String) Returns Value

Class Variables

Generally it is best object-oriented programming practice to avoid the use of class variables.

One situation where I always use class variables is input variables for prompts. The user might be running a series of reports and I need to prompt them for the date range of records to include in the report. In that situation I will use the class variables cDateFrom and cDateTo, so that the next time the user is prompted, the last dates they entered will be prefilled with the last dates they entered. (For as long as they have the application open.)

Class variables are prefixed with lower case c.

Instance Variables

Use instance variable for any values that need to be visible to all of the methods within a class instance.

Instance variables are prefixed with lower case i.

Local Variables

Local variables are only visible within the method they are declared. Good OO practice uses the lowest scope variable needed. If you can use a local variable, do so. As soon as the method is finished the local value is cleared.

Local variables are not prefixed.

Parameter Variables

Parameters are a type of local variable.

Parameter variables are prefixed with lower case p.

pVarName is a parameter variable.

Parameter naming conventions are especially important since the parameter names are automatically copied to the Do statement when you drag a public method from the Interface Manager. For that reason, there are a few additional naming conventions for parameters.

• Field reference type parameters are prefixed with pf. (pfRow, pfList, pfVar)
  
  You can't send ('Hello') as a parameter to a field reference type parameter, so it is important to communicate to the calling method that they must send a variable, not a string in quotes. This also lets the calling method know that the value of that variable in the sender could possibly be changed by the target method. (Although that is best communicated by the method name.)
• Depending on the context of the method name (e.g. $getList), pf prefixed parameters are used to pass a value back to the sender. The variable sent to the method could be empty and the called method then calculates its value. This allows you to return more than one value to a sender, and lets you reserve the return value for the true or false.
• Parameters which require an Omnis constant are prefixed with pk.
  
  pkAlign means send kCenterJst or kRightJst or...
• Boolean parameters are prefixed with pb.
  
  pbRebuildList means send kTrue if you want the list to be rebuilt.)
• Optional parameters are appended with _opt The parameter description should state the default value.

List Variables

If there is an instance variable list or row in a class or superclass that could be defined differently for various instances of that class the names, iList or iRow are used.

If there are more list variables the variables are named to clarify what the data they contain. (iVendorsList, BooksList, AuthorsList).

Note that the plural form of the word is used for the list variable name. (VendorsList not VendorList)

Row variables follow the same naming convention as lists except that they use the singular form of the word. (VendorRow)

At one time I would always use the generic local variable names List or Row in short methods where I felt it was clear enough what the data the list or row variable contained. Since then I changed my practice to using list or row variable names which clearly communicate the data the list or row variable contains.

A coding practice I sometime use is to start with the local variable names List or Row when I write the method and then rename the variable when I finish the code. For example, List is renamed to VendorsList. Omnis kindly changes all occurrances of List to VendorsList for me.

Standard Variable Names

The following are standard variable names:

• FlagOK is a boolean variable used to receive true or false when applicable to the method being called. The initial value is always set to kFalse.
• iList is an instance list variable uses to hold the main data list in a window instance.
• Mssg is a character variable for the message text of an error or prompt message.
• Dtls is a character variable for the additional details text of an error or prompt message.

Variable Prefixes

The following are standard variable name prefixes.

• Item reference variables are prefixed with lowercase r
  
  irButton, rGrid, prWin are item reference variables
• Object datatype variables which point to object classes are prefixed with lowercase o (except task variables)
  
  ioProperties, oExportData are object datatype variables.
• Object Reference datatype variables which point to object classes are prefixed with lowercase or (except task variables)
  
  iorSession, orLogon are object reference datatype variables.
• Boolean variables may be prefixed with lowercase b. Do not name or create a boolean variable that represents a not condition.
  
  Avoid: bNotVisible
  Use: bVisible
• Item reference instance variables which point to a subwindow field are prefixed with irsw
  
  irswAuthorEdit is an item reference variable which points to the subwindow field that instantiates an author edit window.

Variable Suffixes

The following are standard variable name suffixes:

• Obj for SQL related objects. e.g. SessionObj, StmntObj
• CSV for comma separated values.
• Ext for variables which instantiate external objects.
• _opt for optional parameters.

StudioTips Documentation - Copyright 2006 Vencor Software