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fix iterator_input_adapter consuming input before it should #3442

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fix iterator_input_adapter consuming input before it should #3442

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358970e
fix iterator_input_adapter consuming input before it should
Apr 14, 2022
f4a8d2d
tidying up code, no change to logic
Apr 14, 2022
d63d250
Merge branch 'nlohmann:develop' into iterator_input_adapter_fix
imwhocodes Jun 20, 2022
2614b81
Added basic test for the applied fix
Jun 20, 2022
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31 changes: 24 additions & 7 deletions include/nlohmann/detail/input/input_adapters.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -123,6 +123,7 @@ class input_stream_adapter
};
#endif // JSON_NO_IO


// General-purpose iterator-based adapter. It might not be as fast as
// theoretically possible for some containers, but it is extremely versatile.
template<typename IteratorType>
Expand All @@ -132,30 +133,46 @@ class iterator_input_adapter
using char_type = typename std::iterator_traits<IteratorType>::value_type;

iterator_input_adapter(IteratorType first, IteratorType last)
: current(std::move(first)), end(std::move(last))
: current(std::move(first)), end(std::move(last)), current_has_been_consumed(false)
{}

typename std::char_traits<char_type>::int_type get_character()
{
if (JSON_HEDLEY_LIKELY(current != end))

if (JSON_HEDLEY_LIKELY(current_has_been_consumed))
{
auto result = std::char_traits<char_type>::to_int_type(*current);
std::advance(current, 1);
return result;
}

return std::char_traits<char_type>::eof();
if (JSON_HEDLEY_LIKELY(current != end))
{
current_has_been_consumed = true;
return std::char_traits<char_type>::to_int_type(*current);
}
else
{
current_has_been_consumed = false;
return std::char_traits<char_type>::eof();
}

}

private:
IteratorType current;
IteratorType end;
mutable IteratorType current;
const IteratorType end;
mutable bool current_has_been_consumed;

template<typename BaseInputAdapter, size_t T>
friend struct wide_string_input_helper;

bool empty() const
{
if (JSON_HEDLEY_LIKELY(current_has_been_consumed))
{
std::advance(current, 1);
current_has_been_consumed = false;
}

return current == end;
}
};
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31 changes: 24 additions & 7 deletions single_include/nlohmann/json.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5533,6 +5533,7 @@ class input_stream_adapter
};
#endif // JSON_NO_IO


// General-purpose iterator-based adapter. It might not be as fast as
// theoretically possible for some containers, but it is extremely versatile.
template<typename IteratorType>
Expand All @@ -5542,30 +5543,46 @@ class iterator_input_adapter
using char_type = typename std::iterator_traits<IteratorType>::value_type;

iterator_input_adapter(IteratorType first, IteratorType last)
: current(std::move(first)), end(std::move(last))
: current(std::move(first)), end(std::move(last)), current_has_been_consumed(false)
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@falbrechtskirchinger falbrechtskirchinger Apr 14, 2022 •
edited
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You may as well remove the member initializer here, since you've already initialized it in the declaration.

I don't know if clang-tidy, etc. will complain. There're various checks for redundant stuff.

Edit: clang-tidy did in fact complain:
error: member initializer for 'current_has_been_consumed' is redundant

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Maybe it is better to keep it in the constructor (maybe explicitly delete the default constructor) and remove the initialisation in the declaration?

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Maybe it is better to keep it in the constructor (maybe explicitly delete the default constructor) and remove the initialisation in the declaration?

Pick one. I prefer in-class myself, so I'd remove the member initializer as suggested.

The default constructor is implicitly deleted because we have a user-defined constructor, right?

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@imwhocodes imwhocodes Apr 14, 2022 •
edited
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The default constructor is implicitly deleted because we have a user-defined constructor, right?

Yes, this is actually correct

{}

typename std::char_traits<char_type>::int_type get_character()
{
if (JSON_HEDLEY_LIKELY(current != end))

if (JSON_HEDLEY_LIKELY(current_has_been_consumed))
{
auto result = std::char_traits<char_type>::to_int_type(*current);
std::advance(current, 1);
return result;
}

return std::char_traits<char_type>::eof();
if (JSON_HEDLEY_LIKELY(current != end))
{
current_has_been_consumed = true;
return std::char_traits<char_type>::to_int_type(*current);
}
else
{
current_has_been_consumed = false;
return std::char_traits<char_type>::eof();
}
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And clang-tidy doesn't like else after return. It wants this instead:

if (JSON_HEDLEY_LIKELY(current != end))
{
    current_has_been_consumed = true;
    return std::char_traits<char_type>::to_int_type(*current);
}

current_has_been_consumed = false;
return std::char_traits<char_type>::eof();


}

private:
IteratorType current;
IteratorType end;
mutable IteratorType current;
const IteratorType end;
mutable bool current_has_been_consumed;
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@falbrechtskirchinger falbrechtskirchinger Apr 14, 2022 •
edited
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/__w/json/json/include/nlohmann/detail/input/input_adapters.hpp:163:18: error: use default member initializer for 'current_has_been_consumed' [modernize-use-default-member-init,-warnings-as-errors]
    mutable bool current_has_been_consumed;
                 ^
                                          {false}

clang-tidy seems to insist on this:
mutable bool current_has_been_consumed{false};

(Didn't know/remember that.)

CI should turn green after these two changes.

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Please use

mutable bool current_has_been_consumed = false;

This library has a troubled relationship to braced initializers... :-)


template<typename BaseInputAdapter, size_t T>
friend struct wide_string_input_helper;

bool empty() const
{
if (JSON_HEDLEY_LIKELY(current_has_been_consumed))
{
std::advance(current, 1);
current_has_been_consumed = false;
}

return current == end;
}
};
Expand Down