In computer programming, abstraction inversion is an anti-pattern arising when users of a construct need functions implemented within it but not exposed by its interface. The result is that the users re-implement the required functions in terms of the interface, which in its turn uses the internal implementation of the same functions. This may result in implementing lower-level features in terms of higher-level ones, thus the term 'abstraction inversion'. Possible ill-effects are:
The user of such a re-implemented function may seriously underestimate its running-costs.
The user of the construct is forced to obscure their implementation with complex mechanical details.
Many users attempt to solve the same problem, increasing the risk of error.
Examples
Alleged examples from professional programming circles include:
In Ada, choice of the rendezvous construct as a synchronisation primitive forced programmers to implement simpler constructs such as semaphores on the more complex basis.
Like Applesoft BASIC, Lua has a floating-point type as its sole numeric type when configured for desktop computers, and it had no bitwise operators prior to Lua 5.2.
Creating an object to represent a function is cumbersome in object-oriented languages such as Java and C++, in which functions are not first-class objects. In C++ it is possible to make an object 'callable' by overloading the operator, but it is still often necessary to implement a new class, such as the .
Tom Lord has suggested that Subversionversion control system pays for the abstraction inversion of implementing a write-only database on a read/write database with poor performance.
Using stored procedures to manipulate data in a relational database, without granting programmers right to deploy such procedures, leads to reimplementing queries outside the database. For example, large datasets are fetched and actual filtering takes place in application code. Alternatively, thousands of rows are updated one by one instead of running a multiple row query.
Examples that are common outside professional programming circles include:
Using spreadsheet lookup functions to replicate the functionality of a database
