3c7df98c7b
There is a syntax error in the provided code example - this PR fixes it. I did a quick search - I could not find similar _typos_.
75 lines
2.5 KiB
ReStructuredText
75 lines
2.5 KiB
ReStructuredText
.. title:: clang-tidy - performance-enum-size
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performance-enum-size
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=====================
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Recommends the smallest possible underlying type for an ``enum`` or ``enum``
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class based on the range of its enumerators. Analyzes the values of the
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enumerators in an ``enum`` or ``enum`` class, including signed values, to
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recommend the smallest possible underlying type that can represent all the
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values of the ``enum``. The suggested underlying types are the integral types
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``std::uint8_t``, ``std::uint16_t``, and ``std::uint32_t`` for unsigned types,
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and ``std::int8_t``, ``std::int16_t``, and ``std::int32_t`` for signed types.
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Using the suggested underlying types can help reduce the memory footprint of
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the program and improve performance in some cases.
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For example:
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.. code-block:: c++
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// BEFORE
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enum Color {
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RED = -1,
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GREEN = 0,
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BLUE = 1
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};
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std::optional<Color> color_opt;
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The `Color` ``enum`` uses the default underlying type, which is ``int`` in this
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case, and its enumerators have values of -1, 0, and 1. Additionally, the
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``std::optional<Color>`` object uses 8 bytes due to padding (platform
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dependent).
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.. code-block:: c++
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// AFTER
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enum Color : std::int8_t {
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RED = -1,
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GREEN = 0,
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BLUE = 1
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}
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std::optional<Color> color_opt;
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In the revised version of the `Color` ``enum``, the underlying type has been
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changed to ``std::int8_t``. The enumerator `RED` has a value of -1, which can
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be represented by a signed 8-bit integer.
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By using a smaller underlying type, the memory footprint of the `Color`
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``enum`` is reduced from 4 bytes to 1 byte. The revised version of the
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``std::optional<Color>`` object would only require 2 bytes (due to lack of
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padding), since it contains a single byte for the `Color` ``enum`` and a single
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byte for the ``bool`` flag that indicates whether the optional value is set.
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Reducing the memory footprint of an ``enum`` can have significant benefits in
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terms of memory usage and cache performance. However, it's important to
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consider the trade-offs and potential impact on code readability and
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maintainability.
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Enums without enumerators (empty) are excluded from analysis.
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Requires C++11 or above.
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Does not provide auto-fixes.
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Options
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-------
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.. option:: EnumIgnoreList
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Option is used to ignore certain enum types. It accepts a
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semicolon-separated list of (fully qualified) enum type names or regular
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expressions that match the enum type names. The default value is an empty
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string, which means no enums will be ignored.
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