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Ada '83 Rationale, Sec 10.6: Summary and Conclusion

"Rationale for the Design of the
Ada® Programming Language"

[Ada '83 Rationale, HTML Version]

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CHAPTER 10: Separate Compilation and Libraries

10.6 Summary and Conclusion

To summarize the Ada separate compilation facility: Separate compilation has been designed as a user-oriented facility that supports the traditional forms of program development. It can be implemented at reasonable cost, as evidenced by the previous sections and by previous languages supporting a similar separate compilation facility such as Lis and Mesa. The type rules are enforced across separate units to the same degree as within a given unit, and the information contained in a program library can be used to check that the compilation of a given unit does not use information from other units that have become obsolete in the meantime.

Finally, one of the motivations of separate compilation is the creation of software libraries. This is supported by Ada. By far the most useful library units should be packages and generic packages. Ada permits their use with the same degree of safety as for internal units.

It is expected that library packages will be used for the encapsulation of type definitions, for common constants and data, and for shared declarations. The fact that these library items are already compiled program units, rather than source texts, offers a degree of safety not found in languages that provide merely independent compilations.

Other compilation units will be used for the creation of user packages such as input-output packages, to be found in libraries. The ability to compile a package specification separately from the corresponding package body provides the possibility of separating the interface of a package from its implementation. Thus it supports information hiding and reliability to an extremely high degree.

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