Uniform access principle

The uniform access principle of computer programming was put forth by Bertrand Meyer (originally in Object-Oriented Software Construction). It states "All services offered by a module should be available through a uniform notation, which does not betray whether they are implemented through storage or through computation". This principle applies generally to the syntax of object-oriented programming languages. In simpler form, it states that there should be no syntactical difference between working with an attribute, pre-computed property, or method/query of an object.

While most examples focus on the "read" aspect of the principle (i.e., retrieving a value), Meyer shows that the "write" implications (i.e., modifying a value) of the principle are harder to deal with in his monthly column on the Eiffel programming language official website.

The problem being addressed by Meyer involves the maintenance of large software projects or software libraries. Sometimes when developing or maintaining software it is necessary, after much code is in place, to change a class or object in a way that transforms what was simply an attribute access into a method call. Programming languages often use different syntax for attribute access and invoking a method, (e.g., object.something versus object.something()). The syntax change would require, in popular programming languages of the day, changing the source code in all the places where the attribute was used. This might require changing source code in many different locations throughout a very large volume of source code. Or worse, if the change is in an object library used by hundreds of customers, each of those customers would have to find and change all the places the attribute was used in their own code and recompile their programs.

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