See http://www.clopenset.com/content/c-traits-revisited

.gitignore

cpp-traits-v2
cpp-traits-v2.exe

README.md

C++ traits demo

See blog post for more information.

Licence

Project is released under MIT licence.

algorithm.hpp

#pragma once

template<typename Tree> struct OMTraits;

template<typename Tree>
class Algorithm
{
public:
    typedef typename OMTraits<Tree>::Node Node;
    typedef typename OMTraits<Tree>::NodeType NodeType;
    static const NodeType NodeType_TERMINAL = OMTraits<Tree>::NodeType_TERMINAL;
    static const NodeType NodeType_NONTERMINAL = OMTraits<Tree>::NodeType_NONTERMINAL;

    void dumpTree(const Tree &tree) const
    {
        cout << "Tree: " << tree.name() << endl;
        for (typename vector<Node>::const_iterator i = tree.nodes().begin(); i != tree.nodes().end(); ++i)
        {
            dumpNode(*i);
        }
    }

private:
    void dumpNode(const Node &node) const
    {
        cout << "  " << node.name() << ": " << getNodeTypeString(node.type()) << endl;
    }

    string getNodeTypeString(NodeType nodeType) const
    {
        switch (nodeType)
        {
            case NodeType_TERMINAL: return "TERMINAL";
            case NodeType_NONTERMINAL: return "NONTERMINAL";
            default: return "(other)";
        }
    }
};

common.hpp

#pragma once

#include <string>
#include <iostream>
#include <vector>

using namespace std;

LICENSE

The MIT License (MIT)

Copyright (c) 2014 Richard Cook

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

main.cpp

#include "common.hpp"
#include "om1.hpp"
#include "om2.hpp"
#include "algorithm.hpp"

template<>
struct OMTraits<OM1::Tree>
{
    typedef OM1::Node Node;
    typedef OM1::NodeType NodeType;

    // BEGIN: Generated static constants for enums
    static const OM1::NodeType NodeType_TERMINAL = OM1::TERMINAL;
    static const OM1::NodeType NodeType_NONTERMINAL = OM1::NONTERMINAL;
    // END: Generated static constants for enums
};

template<>
struct OMTraits<OM2::Tree>
{
    typedef OM2::Node Node;
    typedef OM2::NodeType NodeType;

    // BEGIN: Generated static constants for enums
    static const OM2::NodeType NodeType_TERMINAL = OM2::TERMINAL;
    static const OM2::NodeType NodeType_NONTERMINAL = OM2::NONTERMINAL;
    // END: Generated static constants for enums
};

// Partial method specialization for type-specific behaviours
template<>
void Algorithm<OM2::Tree>::dumpNode(const Node &node) const
{
    cout << "  [specialized behaviour] " << node.name() << ": " << getNodeTypeString(node.type()) << endl;
}

int main()
{
    OM1::Tree tree1("OM1::Tree");
    tree1.addNode(OM1::Node("OM1::Node1", OM1::TERMINAL));
    tree1.addNode(OM1::Node("OM1::Node2", OM1::NONTERMINAL));
    Algorithm<OM1::Tree> algorithm1;
    algorithm1.dumpTree(tree1);

    OM2::Tree tree2("OM2::Tree");
    tree2.addNode(OM2::Node("OM2::Node1", OM2::TERMINAL));
    tree2.addNode(OM2::Node("OM2::Node2", OM2::NONTERMINAL));
    Algorithm<OM2::Tree> algorithm2;
    algorithm2.dumpTree(tree2);

    return 0;
}

Makefile

CPP := g++
TARGET := cpp-traits-v2

all: $(TARGET)

$(TARGET): main.cpp *.hpp
	$(CPP) -o $@ main.cpp

.PHONY: clean
clean:
	rm -f $(TARGET)

om1.hpp

#pragma once

namespace OM1
{
    // Same enum member names as ObjectModel2::NodeType but different values
    enum NodeType { TERMINAL = 100, NONTERMINAL = 101 };

    class Node
    {
    public:
        Node(const string &name, NodeType type) : m_name(name), m_type(type) { }
        const string &name() const { return m_name; }
        NodeType type() const { return m_type; }

    private:
        string m_name;
        NodeType m_type;
    };

    class Tree
    {
    public:
        Tree(const string &name) : m_name(name) { }
        const string &name() const { return m_name; }
        const vector<Node> &nodes() const { return m_nodes; }
        void addNode(const Node &node) { m_nodes.push_back(node); }

    private:
        string m_name;
        vector<Node> m_nodes;
    };
}

om2.hpp

#pragma once

namespace OM2
{
    // Same enum member names as ObjectModel1::NodeType but different values
    enum NodeType { TERMINAL = 200, NONTERMINAL = 201 };

    class Node
    {
    public:
        Node(const string &name, NodeType type) : m_name(name), m_type(type) { }
        const string &name() const { return m_name; }
        NodeType type() const { return m_type; }

    private:
        string m_name;
        NodeType m_type;
    };

    class Tree
    {
    public:
        Tree(const string &name) : m_name(name) { }
        const string &name() const { return m_name; }
        const vector<Node> &nodes() const { return m_nodes; }
        void addNode(const Node &node) { m_nodes.push_back(node); }

    private:
        string m_name;
        vector<Node> m_nodes;
    };
}