Concepts

A concept is a name for a set of type requirements. A concrete type adhering to these requirements is said to model the concept. For example, an Array concept can be defined in terms of requirements like this (there will be more requirements):

• There must be a nested type called Element, defining the type of the elements

• There must be a member function called rank, returning the dimensionality as an integral

• There must be a member function called extents, returning a collection of extents in each dimension

Depending on the programming language, it may be possible to enforce concepts. In C++ concepts can be used to constrain type parameters of class and function templates. The template can then only be instantiated by types modelling the concept, and if they don’t, a relevant error message can be shown by the compiler. In Python, concepts are not a thing, but type hints and duck typing are related.

In any case, concepts can be documented, and used to describe types that can be passed into functions, for example. That is what these pages are intended for. Since LUE contains operations and types that can be used from multiple programming languages, instead of documenting each language specific API, duplicating a lot of text, the LUE documentation is written in terms of language agnostic operations, concepts, and types modelling these concepts. Since examples are included for the various supported programming languages, it is hoped that the user can infer how to use LUE operations from a specific language.

Note

Concepts in C++ make it possible to implement LUE in terms of types it does not know about. As long as those types adhere to the requirements of the concepts used by LUE, all should be fine. This makes it possible, for example, to compile a LUE version that uses types for representing rasters that are part of other software packages, like QGIS. This allows LUE to be integrated very tightly into other packages.