Ichthyostega
806db414dd
* Lumiera source code always was copyrighted by individual contributors * there is no entity "Lumiera.org" which holds any copyrights * Lumiera source code is provided under the GPL Version 2+ == Explanations == Lumiera as a whole is distributed under Copyleft, GNU General Public License Version 2 or above. For this to become legally effective, the ''File COPYING in the root directory is sufficient.'' The licensing header in each file is not strictly necessary, yet considered good practice; attaching a licence notice increases the likeliness that this information is retained in case someone extracts individual code files. However, it is not by the presence of some text, that legally binding licensing terms become effective; rather the fact matters that a given piece of code was provably copyrighted and published under a license. Even reformatting the code, renaming some variables or deleting parts of the code will not alter this legal situation, but rather creates a derivative work, which is likewise covered by the GPL! The most relevant information in the file header is the notice regarding the time of the first individual copyright claim. By virtue of this initial copyright, the first author is entitled to choose the terms of licensing. All further modifications are permitted and covered by the License. The specific wording or format of the copyright header is not legally relevant, as long as the intention to publish under the GPL remains clear. The extended wording was based on a recommendation by the FSF. It can be shortened, because the full terms of the license are provided alongside the distribution, in the file COPYING.
90 lines
3.6 KiB
C++
90 lines
3.6 KiB
C++
/*
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BUILDER-QUALIFIER-SUPPORT.hpp - accept arbitrary qualifier terms for builder functions
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Copyright (C)
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2022, Hermann Vosseler <Ichthyostega@web.de>
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**Lumiera** is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2 of the License, or (at your
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option) any later version. See the file COPYING for further details.
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*/
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/** @file builder-qualifier-support.hpp
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** Mix-in to support builder functions to accept optional qualifier terms.
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** For the classical _builder pattern_ we define a dedicated *builder* class,
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** which in turn offers explicitly named setter or configuration functions.
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** However, sometimes it is desirable just to offer some builder-like extension
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** on regular constructor syntax, where optional additional parameters may be passed
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** to adapt the basic setup. Unfortunately, a list of optional further argument tends
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** to become hard to read, especially when some dummy arguments must be passed in order
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** to supply a setting further down the list.
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**
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** This mix-in template instead allows to define _qualifier terms,_ and to pass an arbitrary
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** sequence of such terms to a constructor or builder function. These qualifiers look like
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** "algebraic data types" at invocation site, i.e. they are named terms, optionally even accepting
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** further arguments. Yet for the implementation, these qualifiers return a wrapped functor. When
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** defined as _friend function,_ the generated qualifier functors may even manipulate private internals
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** of the "Builder" or "Strategy" class.
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** @warning since these qualifiers manipulate by side-effect, it is up to the user to ensure
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** consistent settings and behaviour (typically within a terminal `build()` function).
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** @note the `qualify()` function accepts the qualifier functors by-reference; thus it is up
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** to the user to either pass them by-value, by reverence or even by perfect forwarding.
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**
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** @see BuilderQualifierSupport_test
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** @see ElementBoxWidget as usage example
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*/
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#ifndef LIB_BUILDER_QUALIFIER_SUPPORT_H
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#define LIB_BUILDER_QUALIFIER_SUPPORT_H
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#include <functional>
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namespace lib {
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/**
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* Mix-in to accept and apply an arbitrary sequence of qualifier functors.
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* Typically these are used for Builder or Strategy definitions and applied
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* to some target object, which thereby is manipulated by the qualifiers by
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* side-effect.
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* @tparam TAR target type to apply the qualifier functors
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* @remark the intended usage is to mix-in this template privately and then
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* to define _qualifier friend functions,_ each binding a suitable lambda
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* to manipulate the internal settings. This way, at usage site, an arbitrary
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* sequence of clearly labelled "algebraic terms" can be accepted, to tweak
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* and adapt the basic features established on the Builder or Strategy.
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*/
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template<class TAR>
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class BuilderQualifierSupport
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{
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protected:
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using Manipulator = std::function<void(TAR&)>;
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struct Qualifier
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: Manipulator
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{
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using Manipulator::Manipulator;
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};
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/** Main entrance point: apply the given qualifiers in sequence to the `target`. */
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template<class... QUALS>
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friend void qualify(TAR& target, Qualifier& qualifier, QUALS& ...qs)
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{
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qualifier(target);
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qualify(target, qs...);
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}
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friend void qualify(TAR&){ }
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public:
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// default construct and copyable
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};
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}// namespace lib
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#endif /*LIB_BUILDER_QUALIFIER_SUPPORT_H*/
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