source: src/AST/Node.hpp@ f47f887

#pragma once

#include <memory>

namespace ast {
class Node {
public:
        virtual ~Node() = default;

        enum class ref_type {
                strong,
                weak
        };

        inline void increment(ref_type ref) const {
                switch (ref) {
                        case ref_type::strong: strong_ref++; break;
                        case ref_type::weak  : weak_ref  ++; break;
                }
        }

        inline void decrement(ref_type ref) const {
                switch (ref) {
                        case ref_type::strong: strong_ref--; break;
                        case ref_type::weak  : weak_ref  --; break;
                }

                if(!strong_ref && !weak_ref) {
                        delete this;
                }
        }

        template<typename node_t>
        friend auto mutate(const node_t * node);

private:
        mutable size_t strong_ref = 0;
        mutable size_t weak_ref = 0;
};

// Mutate a node, non-member function to avoid static type
// problems and be able to use auto return
template<typename node_t>
auto mutate(const node_t * node) {
        assertf(
                node->strong_count >= 1,
                "Error: attempting to mutate a node that appears to have been linked"
        );
        if (node->strong_count == 1) {
                return const_cast<node_t *>(node);
        }

        assertf(
                node->weak_count == 0,
                "Error: mutating node with weak references to it will invalided some references"
        );
        return node->clone();
}

// Base class for the smart pointer types
// should never really be used.
template< typename node_t, enum Node::ref_type ref_t>
class ptr_base {
public:
        ptr_base() : node(nullptr) {}
        ptr_base( node_t * n ) : node(n) { if( !node ) node->increment(ref_t); }
        ~ptr_base() { if( node ) node->decrement(ref_t); }

        template< enum  Node::ref_type o_ref_t >
        ptr_base( const ptr_base<node_t, o_ref_t> & o ) : node(o.node) {
                if( !node ) return;
                node->increment(ref_t);
        }

        template< enum  Node::ref_type o_ref_t >
        ptr_base( ptr_base<node_t, o_ref_t> && o ) : node(o.node) {
                if( node ) node->increment(ref_t);
                if( node ) node->decrement(o_ref_t);
        }

        template< enum  Node::ref_type o_ref_t >
        ptr_base & operator=( const ptr_base<node_t, o_ref_t> & o ) {
                assign(o.node);
                return *this;
        }

        template< enum  Node::ref_type o_ref_t >
        ptr_base & operator=( ptr_base<node_t, o_ref_t> && o ) {
                if(o.node == node) return *this;
                assign(o.node);
                if( node ) node->decrement(o_ref_t);
                return *this;
        }

        const node_t * get() const { return  node; }
        const node_t * operator->() const { return  node; }
        const node_t & operator* () const { return *node; }
        explicit operator bool() const { return node; }
        operator const node_t * const() const { return node; }

        using ptr = const node_t *;

private:
        void assign(node_t * other ) {
                if( other ) other->increment(ref_t);
                if( node  ) node ->decrement(ref_t);
                node = other;
        }

protected:
        node_t * node;
};

template< typename node_t >
using ptr = ptr_base< node_t, Node::ref_type::strong >;

template< typename node_t >
using readonly = ptr_base< node_t, Node::ref_type::weak >;
}