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Merge pull request #10873 from Calinou/cpp-usage-guidelines-stl-datatypes
Add a table listing STL datatypes and their Godot equivalents in C++ usage guidelines
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‎contributing/development/cpp_usage_guidelines.rst

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@@ -53,18 +53,72 @@ as Godot provides its own data types (among other things).
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See :ref:`doc_faq_why_not_stl` for more information.
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This means that pull requests should **not** use ``std::string``,
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``std::vector`` and the like. Instead, use Godot's datatypes as described below:
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- Use ``String`` instead of ``std::string``.
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- Use ``Vector`` instead of ``std::vector``. In some cases, ``LocalVector``
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can be used as an alternative (ask core developers first).
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- Use ``Array`` instead of ``std::array``.
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.. note::
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Godot also has a List datatype (which is a linked list). While List is already used
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in the codebase, it typically performs worse than other datatypes like Vector
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and Array. Therefore, List should be avoided in new code unless necessary.
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``std::vector`` and the like. Instead, use Godot's datatypes as described below.
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A 📜 icon denotes the type is part of :ref:`Variant <doc_variant_class>`. This
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means it can be used as a parameter or return value of a method exposed to the
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scripting API.
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| Godot datatype | Closest C++ STL datatype | Comment |
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+========================+==========================+=======================================================================================+
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| ``String`` 📜 | ``std::string`` | **Use this as the "default" string type.** ``String`` uses UTF-32 encoding |
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| | | to improve performance thanks to its fixed character size. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``StringName`` 📜 | ``std::string`` | Uses string interning for fast comparisons. Use this for static strings that are |
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| | | referenced frequently and used in multiple locations in the engine. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``Vector`` | ``std::vector`` | **Use this as the "default" vector type.** Uses copy-on-write (COW) semantics. |
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| | | This means it's generally slower but can be copied around almost for free. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``LocalVector`` | ``std::vector`` | Closer to ``std::vector`` in semantics. In most situations, ``Vector`` should be |
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| | | preferred. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``Array`` 📜 | ``std::vector`` | Values can be of any Variant type. No static typing is imposed. |
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| | | Uses shared reference counting, similar to ``std::shared_ptr``. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``TypedArray`` 📜 | ``std::vector`` | Subclass of ``Array`` but with static typing for its elements. |
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| | | Not to be confused with ``Packed*Array``, which is internally a ``Vector``. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``Packed*Array`` 📜 | ``std::vector`` | Alias of ``Vector``, e.g. ``PackedColorArray = Vector<Color>``. |
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| | | Only a limited list of packed array types are available |
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| | | (use ``TypedArray`` otherwise). |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``List`` | ``std::list`` | Linked list type. Generally slower than other array/vector types. Prefer using |
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| | | other types in new code, unless using ``List`` avoids the need for type conversions. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``Span`` | ``std::span`` | Represents read-only access to a contiguous array without needing to copy any data. |
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| | | See `pull request description <https://github.com/godotengine/godot/pull/100293>`__ |
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| | | for details. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``HashSet`` | ``std::unordered_set`` | **Use this as the "default" set type.** |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``RBSet`` | ``std::set`` | Uses a `red-black tree <https://en.wikipedia.org/wiki/Red-black_tree>`__ |
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| | | for faster access. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``VSet`` | ``std::flat_set`` | Uses copy-on-write (COW) semantics. |
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| | | This means it's generally slower but can be copied around almost for free. |
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| | | The performance benefits of ``VSet`` aren't established, so prefer using other types. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``HashMap`` | ``std::unordered_map`` | **Use this as the "default" map type.** Does not preserve insertion order. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``AHashMap`` | ``std::unordered_map`` | Array-based implementation of a hash map. Does not preserve insertion order. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``OAHashMap`` | ``std::unordered_map`` | Does not preserve insertion order. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``RBMap`` | ``std::map`` | Uses a `red-black tree <https://en.wikipedia.org/wiki/Red-black_tree>`__ |
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| | | for faster access. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``VMap`` | ``std::flat_map`` | Uses copy-on-write (COW) semantics. |
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| | | This means it's generally slower but can be copied around almost for free. |
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| | | The performance benefits of ``VMap`` aren't established, so prefer using other types. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``Dictionary`` 📜 | ``std::unordered_map`` | Keys and values can be of any Variant type. No static typing is imposed. |
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| | | Uses shared reference counting, similar to ``std::shared_ptr``. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``TypedDictionary`` 📜 | ``std::unordered_map`` | Subclass of ``Dictionary`` but with static typing for its keys and values. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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| ``Pair`` | ``std::pair`` | Stores a single key-value pair. |
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+------------------------+--------------------------+---------------------------------------------------------------------------------------+
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``auto`` keyword
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~~~~~~~~~~~~~~~~

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