Chapter 3: Readability - TOC - 3.2 NAMING CONVENTIONS

3.2.3 Object Names

guideline

Use predicate clauses or adjectives for Boolean objects.

Use singular, specific nouns as object identifiers.

Choose identifiers that describe the object's value during execution.

Use singular, general nouns as identifiers for record components.

example

Non-Boolean objects:

Today           : Day;
Yesterday       : Day;
Retirement_Date : Date;

Boolean objects:

User_Is_Available : Boolean;        -- predicate clause
List_Is_Empty     : Boolean;        -- predicate clause
Empty             : Boolean;        -- adjective
Bright            : Boolean;        -- adjective

rationale

Using specific nouns for objects establishes a context for understanding the object's value, which is one of the general values described by the subtype's name (see Guideline 3.2.2). Object declarations become very English-like with this style. For example, the first declaration above is read as "Today is a Day."

General nouns, rather than specific, are used for record components because a record object's name will supply the context for understanding the component. Thus, the following component is understood as "the year of retirement":

Retirement_Date.Year

Following conventions that relate object types and parts of speech makes code read more like text. For example, because of the names chosen, the following code segment needs no comments:

if List_Is_Empty then
   Number_Of_Elements := 0;
else
   Number_Of_Elements := Length_Of_List;
end if;

notes

If it is difficult to find a specific noun that describes an object's value during the entire execution of a program, the object is probably serving multiple purposes. Multiple objects should be used in such a case.