It is a pure object-oriented computer software language system that closely follows Dr. Meyer's work in Object Oriented Software Construction, Second Edition. Eiffel differs from most popular languages in several ways.
The goal of the language, libraries, and programing methods is to create reliable, reusable software modules. It supports multiple inheritance, genericity?, polymorphism, and encapsulation?. It's most important contribution to software engineering is Design by Contract, where assertions?, preconditions?, and postconditions? are used to assist in documenting program correctness. There are free versions available, check a web directory for links.
First, Eiffel employs Design by Contract theory and technology. Design by Contract (or DBC) is the concept that classes have obligations to other classes based upon formalized rules between them. All class relationships are between Client classes and Supplier classes. A Client class is obligated to make calls to Supplier features where the resulting state of the Supplier is not violated by the Client call. Subsequently, the Supplier is obligated to provide a return state and data that does not violate the state requirements of the Client. For instance, a Supplier data buffer may require that data is present in the buffer when a delete feature is called. Subsequently, the Supplier guarantees to the client that when a delete feature finishes its work, the data item will, indeed, be deleted from the buffer. Other Design Contracts are concepts of "Class Invariant". The Class Invariant guarantees (for the local class) that the state of the class will be maintained within specified tolerances at the end of each feature execution.
Second, Eiffel offers multiple class inheritance. Many people have objections to multiple inheritance. The Eiffel implementation of multiple inheritance overcomes these objections as the result of careful study, proper theory, and mindful implementation. A simplistic treatment of Multiple Inheritance leads to problems. However, by following some simple rules, all of these issues are resolved, and multiple inheritance becomes a useful tool.
Last, Eiffel is an excellent implementation of pure OOP theory. The language has formal support for abstract data types. In accordance with Self Documentation, a software text should be able to reproduce its design documentation from the text itself. Eiffel accomplishes this by using a formalized implementation of the Abstract Data Type.
Moreover, if you use the Eiffel Studio software development platform, you will discover an environment where software engineering is performed in an object-oriented interface.
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