Editing Parameter (computer programming) (section)

===Alternative convention in Eiffel===
Within the [[Eiffel (programming language)|Eiffel]] software development method and language, the terms ''argument'' and ''parameter'' have distinct uses established by convention. The term ''argument'' is used exclusively in reference to a routine's inputs,<ref>Meyer, Bertrand. ''[[Object-Oriented Software Construction]], 2nd Edition,'' Prentice Hall, 1997, p 444.</ref> and the term ''parameter'' is used exclusively in type parameterization for [[Generic programming|generic classes]].<ref>Meyer, p. 96.</ref>

Consider the following routine definition:

<syntaxhighlight lang="eiffel">
    sum (addend1: INTEGER; addend2: INTEGER): INTEGER
        do
            Result := addend1 + addend2
        end
</syntaxhighlight>

The routine <code>sum</code> takes two arguments <code>addend1</code> and <code>addend2</code>, which are called the routine's '''formal arguments'''.  A call to <code>sum</code> specifies '''actual arguments''', as shown below with <code>value1</code> and <code>value2</code>.

<syntaxhighlight lang="eiffel">
    sum_value: INTEGER
    value1: INTEGER = 40
    value2: INTEGER = 2
                …
            sum_value := sum (value1, value2)    
</syntaxhighlight>

Parameters are also thought of as either '''formal''' or '''actual'''. '''Formal generic parameters''' are used in the definition of generic classes. In the example below, the class <code>HASH_TABLE</code>  is declared as a generic class which has two formal generic parameters, <code>G</code> representing data of interest and <code>K</code> representing the hash key for the data:

<syntaxhighlight lang="eiffel">
class HASH_TABLE [G, K -> HASHABLE] 
            …
</syntaxhighlight>

When a class becomes a client to <code>HASH_TABLE</code>, the formal generic parameters are substituted with '''actual generic parameters''' in a '''generic derivation'''. In the following attribute declaration, <code>my_dictionary</code> is to be used as a character string based [[Associative array|dictionary]]. As such, both data and key formal generic parameters are substituted with actual generic parameters of type <code>STRING</code>.

<syntaxhighlight lang="eiffel">
    my_dictionary: HASH_TABLE [STRING, STRING] 
</syntaxhighlight>