1// Copyright 2011 Google Inc.
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28
29#include <cassert>
30#include <cstring>
31
32#include "stack_cleaner.hpp"
33#include "state.ipp"
34
35
36/// Internal implementation for lutok::stack_cleaner.
37struct lutok::stack_cleaner::impl {
38    /// Reference to the Lua state this stack_cleaner refers to.
39    state& state_ref;
40
41    /// The depth of the Lua stack to be restored.
42    unsigned int original_depth;
43
44    /// Constructor.
45    ///
46    /// \param state_ref_ Reference to the Lua state.
47    /// \param original_depth_ The depth of the Lua stack.
48    impl(state& state_ref_, const unsigned int original_depth_) :
49        state_ref(state_ref_),
50        original_depth(original_depth_)
51    {
52    }
53};
54
55
56/// Creates a new stack cleaner.
57///
58/// This gathers the current height of the stack so that extra elements can be
59/// popped during destruction.
60///
61/// \param state_ The Lua state.
62lutok::stack_cleaner::stack_cleaner(state& state_) :
63    _pimpl(new impl(state_, state_.get_top()))
64{
65}
66
67
68/// Pops any values from the stack not known at construction time.
69///
70/// \pre The current height of the stack must be equal or greater to the height
71/// of the stack when this object was instantiated.
72lutok::stack_cleaner::~stack_cleaner(void)
73{
74    const unsigned int current_depth = _pimpl->state_ref.get_top();
75    assert(current_depth >= _pimpl->original_depth);
76    const unsigned int diff = current_depth - _pimpl->original_depth;
77    if (diff > 0)
78        _pimpl->state_ref.pop(diff);
79}
80
81
82/// Forgets about any elements currently in the stack.
83///
84/// This allows a function to return values on the stack because all the
85/// elements that are currently in the stack will not be touched during
86/// destruction when the function is called.
87void
88lutok::stack_cleaner::forget(void)
89{
90    _pimpl->original_depth = _pimpl->state_ref.get_top();
91}
92