124 lines
4.1 KiB
C++
124 lines
4.1 KiB
C++
/* -*- C++ -*-
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* Serene Programming Language
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*
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* Copyright (c) 2019-2022 Sameer Rahmani <lxsameer@gnu.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* This is a CRTP based Trait implementation that allows to use Trait like
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* classes to create polymorphic functions and API statically at compile type
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* without any runtime shenanigans. For more on CRTP checkout:
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*
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* https://en.wikipedia.org/wiki/Curiously_recurring_template_pattern
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*
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* In order to define a trait, use the `TraitBase` class like:
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* \code
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* template <typename ConcreteType>
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* class Blahable : public TraitBase<ConcreteType, Blahable> {}
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* \endcode
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*
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* Every Trait has to take the `ConcreteType` as template argument and pass it
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* to the `TraitBase`. Checkout the documentation of `TraitBase` for more info
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* on creating a new Trait.
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*
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* Alongside with each Trait type, you should provide the "Official" interface
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* of the Trait via some standalone functions that operates on the Trait type.
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* For example Imagine we have a Trait type called `ABC` with two main
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* functionality `foo` and `bar`. We need to create two functions as follows:
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*
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* \code
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* template <typename T>
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* SomeType Foo(ABC<T> &t) { return t.foo(); };
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*
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* template <typename T>
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* SomeType bar(ABC<T> &t, int x) { return t.bar(x); };
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* \endcode
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*
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* These two functions will be the official interface to the trait `ABC`.
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* IMPORTANT NOTE: Make sure to pass a reference of type `ABC<T>` to the
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* functions and DO NOT PASS BY COPY. Since copying will copy the value by the
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* trait type only, we would not be able to statically case it to the
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* implementor type and it will lead to some allocation problem.
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*
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* Traits can be used via `WithTrait` helper class which provides a clean
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* interface to mix and match Trait types.
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*
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*/
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#ifndef SERENE_TRAITS_H
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#define SERENE_TRAITS_H
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#include <type_traits>
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#include <string>
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namespace serene {
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/// A placeholder structure that replaces the concrete type of the
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/// Imlementations Which might have child classes.
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struct FinalImpl;
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/// In order to use Traits, we can use `WithTrait` class as the base
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/// of any implementation class and pass the Trait classes as template argument
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/// for example:
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///
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/// \code
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/// class Expression : public WithTrait<Expression, Printable, Locatable> {}
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/// \endcode
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template <typename ConcreteType, template <typename T> class... Traits>
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class WithTrait : public Traits<ConcreteType>... {
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protected:
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WithTrait(){};
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friend ConcreteType;
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};
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/// This class provides the common functionality among the Trait Types and
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/// every Trait has to inherit from this class. Here is an example:
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///
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/// \code
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/// template <typename ConcreteType>
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/// class Blahable : public TraitBase<ConcreteType, Blahable> {}
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/// \endcode
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///
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/// In the Trait class the underlaying object which implements the Trait
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/// is accessable via the `Object` method.
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template <typename ConcreteType, template <typename> class TraitType>
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class TraitBase {
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protected:
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/// Statically casts the object to the concrete type object to be
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/// used in the Trait Types.
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// const ConcreteType &Object() const {
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// return static_cast<const ConcreteType &>(*this);
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// };
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ConcreteType &Object() { return static_cast<ConcreteType &>(*this); };
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};
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template <typename ConcreteType>
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class IDebuggable : public TraitBase<ConcreteType, IDebuggable> {
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public:
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IDebuggable(){};
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IDebuggable(const IDebuggable &) = delete;
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std::string toString() const { return this->Object().toString(); }
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};
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template <typename T>
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std::string toString(IDebuggable<T> &t) {
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return t.toString();
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}
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}; // namespace serene
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#endif
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