Pattern-Oriented Software Architecture, A System of Patterns

Chapter 4Idioms

“A what?” he said.“An S.E.P.”“An S…?””… E.P.”“And what’s that?”

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Idioms are low-level patterns specific to a programming language. An idiom describes how to implement particular aspects of components or the relationships between them with the features of the given language.

In this chapter we provide an overview of the use of idioms, show how they can define a programming style, and show where you can find idioms. We refer mainly to other people’s work instead of documenting our own idioms. We do however present the Counted Pointer idiom as a complete idiom description.

4.1 Introduction

Idioms represent low-level patterns. In contrast to design patterns, which address general structural principles, idioms describe how to solve implementation-specific problems in a programming language, such as memory management in C++. Idioms can also directly address the concrete implementation of a specific design pattern. We cannot therefore draw a clear line between design patterns and idioms. Idioms can address low-level problems related to the use of a language, such as naming program elements, source text formatting or choosing return values. Such idioms approach or overlap areas that are typically addressed by programming guidelines. To summarize, we can say that idioms demonstrate competent use of programming language features. Idioms can therefore also support the teaching of a programming language.

A programming ...