xref: /netbsd-src/external/bsd/lutok/dist/stack_cleaner.hpp (revision 8665e60721afffabfeff093f9bdaf33398c3cacb)

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/// \file stack_cleaner.hpp
/// Provides the stack_cleaner class.

#if !defined(LUTOK_STACK_CLEANER_HPP)
#define LUTOK_STACK_CLEANER_HPP

#include <memory>

#include <lutok/state.hpp>

namespace lutok {


/// A RAII model for values on the Lua stack.
///
/// At creation time, the object records the current depth of the Lua stack and,
/// during destruction, restores the recorded depth by popping as many stack
/// entries as required.  As a corollary, the stack can only grow during the
/// lifetime of a stack_cleaner object (or shrink, but cannot become shorter
/// than the depth recorded at creation time).
///
/// Use this class as follows:
///
/// state s;
/// {
///     stack_cleaner cleaner1(s);
///     s.push_integer(3);
///     s.push_integer(5);
///     ... do stuff here ...
///     for (...) {
///         stack_cleaner cleaner2(s);
///         s.load_string("...");
///         s.pcall(0, 1, 0);
///         ... do stuff here ...
///     }
///     // cleaner2 destroyed; the result of pcall is gone.
/// }
/// // cleaner1 destroyed; the integers 3 and 5 are gone.
///
/// You must give a name to the instantiated objects even if they cannot be
/// accessed later.  Otherwise, the instance will be destroyed right away and
/// will not have the desired effect.
class stack_cleaner {
    struct impl;

    /// Pointer to the shared internal implementation.
    std::unique_ptr< impl > _pimpl;

    /// Disallow copies.
    stack_cleaner(const stack_cleaner&);

    /// Disallow assignment.
    stack_cleaner& operator=(const stack_cleaner&);

public:
    stack_cleaner(state&);
    ~stack_cleaner(void);

    void forget(void);
};


}  // namespace lutok

#endif  // !defined(LUTOK_STACK_CLEANER_HPP)