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12. Generic Units

12. Generic Units

1
A generic unit is a program unit that is either a generic subprogram or a generic package. A generic unit is a template, which is parameterized or not, and from which corresponding (nongeneric) subprograms or packages can be obtained. The resulting program units are said to be instances of the original generic unit.

2
A generic unit is declared by a generic declaration. This form of declaration has a generic formal part declaring any generic formal parameters. An instance of a generic unit is obtained as the result of a generic instantiation with appropriate generic actual parameters for the generic formal parameters. An instance of a generic subprogram is a subprogram. An instance of a generic package is a package.

3
Generic units are templates. As templates they do not have the properties that are specific to their nongeneric counterparts. For example, a generic subprogram can be instantiated but it cannot be called. In contrast, the instance of a generic subprogram is a nongeneric subprogram; hence, this instance can be called but it cannot be used to produce further instances.

4
References:

*
declaration 3.1

*
generic actual parameter 12.3

*
generic declaration 12.1

*
generic formal parameter 12.1

*
generic formal part 12.1

*
generic instantiation 12.3

*
generic package 12.1

*
generic subprogram 12.1

*
instance 12.3

*
package 7

*
program unit 6

*
subprogram 6



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