InstanceId.h

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/*
 * Copyright (C) 1996-2020 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */
 
#ifndef SQUID_BASE_INSTANCE_ID_H
#define SQUID_BASE_INSTANCE_ID_H
 
#include <iosfwd>
 
class ScopedId
{
public:
    ScopedId(): scope(nullptr), value(0) {}
    explicit ScopedId(const char *s): scope(s), value(0) {}
    // when the values is zero/unknown, use other constructors
    ScopedId(const char *s, uint64_t v): scope(s), value(v) { /* assert(value) */ }
 
    const char *scope;
 
    uint64_t value;
};
 
std::ostream &operator <<(std::ostream &os, const ScopedId &id);
 
typedef unsigned int InstanceIdDefaultValueType;
template <class Class, class ValueType = InstanceIdDefaultValueType>
class InstanceId
{
public:
    typedef ValueType Value; 
 
    InstanceId() {change();}
 
    operator Value() const { return value; }
    bool operator ==(const InstanceId &o) const { return value == o.value; }
    bool operator !=(const InstanceId &o) const { return !(*this == o); }
    void change();
 
    std::ostream &print(std::ostream &) const;
 
    // TODO: Refactor into static Scope().
    const char * prefix() const;
 
    ScopedId detach() const { return ScopedId(prefix(), value); }
 
public:
    Value value = Value(); 
 
private:
    InstanceId(const InstanceId &); 
    InstanceId& operator=(const InstanceId &); 
};
 
#define InstanceIdDefinitions3(Class, pfx, ValueType, ...) \
    template<> const char * \
    InstanceId<Class, ValueType>::prefix() const { \
        return pfx; \
    } \
    template<> std::ostream & \
    InstanceId<Class, ValueType>::print(std::ostream &os) const { \
        return os << pfx << value; \
    } \
    template<> void \
    InstanceId<Class, ValueType>::change() { \
        static auto Last = Value(); \
        value = ++Last ? Last : ++Last; \
    }
 
#define InstanceIdDefinitions(...) InstanceIdDefinitions3(__VA_ARGS__, InstanceIdDefaultValueType)
 
template <class Class, class ValueType>
inline
std::ostream &operator <<(std::ostream &os, const InstanceId<Class, ValueType> &id)
{
    return id.print(os);
}
 
#endif /* SQUID_BASE_INSTANCE_ID_H */