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XPCOM Collections
=================
``nsTArray`` and ``AutoTArray``
-------------------------------
``nsTArray<T>`` is a typesafe array for holding various objects, similar to ``std::vector<T>``. (note that
``nsTArray<T>`` is dynamically-sized, unlike ``std::array<T>``) Here's an
incomplete list of mappings between the two:
================== ==================================================
std::vector<T> nsTArray<T>
================== ==================================================
``size()`` ``Length()``
``empty()`` ``IsEmpty()``
``resize()`` ``SetLength()`` or ``SetLengthAndRetainStorage()``
``capacity()`` ``Capacity()``
``reserve()`` ``SetCapacity()``
``push_back()`` ``AppendElement()``
``insert()`` ``AppendElements()``
``emplace_back()`` ``EmplaceBack()``
``clear()`` ``Clear()`` or ``ClearAndRetainStorage()``
``data()`` ``Elements()``
``at()`` ``ElementAt()``
``back()`` ``LastElement()``
================== ==================================================
Rust Bindings
~~~~~~~~~~~~~
When the ``thin_vec`` crate is built in Gecko, ``thin_vec::ThinVec<T>`` is
guaranteed to have the same memory layout and allocation strategy as
``nsTArray``, meaning that the two types may be used interchangeably across
FFI boundaries. The type is **not** safe to pass by-value over FFI
boundaries, due to Rust and C++ differing in when they run destructors.
The element type ``T`` must be memory-compatible with both Rust and C++ code
to use over FFI.
``nsTHashMap`` and ``nsTHashSet``
---------------------------------
These types are the recommended interface for writing new XPCOM hashmaps and
hashsets in XPCOM code.
Supported Hash Keys
~~~~~~~~~~~~~~~~~~~
The following types are supported as the key parameter to ``nsTHashMap`` and
``nsTHashSet``.
========================== ======================
Type Hash Key
========================== ======================
``T*`` ``nsPtrHashKey<T>``
``T*`` ``nsPtrHashKey<T>``
``nsCString`` ``nsCStringHashKey``
``nsString`` ``nsStringHashKey``
``uint32_t`` ``nsUint32HashKey``
``uint64_t`` ``nsUint64HashKey``
``intptr_t`` ``IntPtrHashKey``
``nsCOMPtr<nsISupports>`` ``nsISupportsHashKey``
``RefPtr<T>`` ``nsRefPtrHashKey<T>``
``nsID`` ``nsIDHashKey``
========================== ======================
Any key not in this list must inherit from the ``PLDHashEntryHdr`` class to
implement manual hashing behaviour.
Class Reference
~~~~~~~~~~~~~~~
.. note::
The ``nsTHashMap`` and ``nsTHashSet`` types are not declared exactly like
this in code. This is intended largely as a practical reference.
.. cpp:class:: template<K, V> nsTHashMap<K, V>
The ``nsTHashMap<K, V>`` class is currently defined as a thin type alias
around ``nsBaseHashtable``. See the methods defined on that class for
more detailed documentation.
.. cpp:function:: uint32_t Count() const
.. cpp:function:: bool IsEmpty() const
.. cpp:function:: bool Get(KeyType aKey, V* aData) const
Get the value, returning a flag indicating the presence of the entry
in the table.
.. cpp:function:: V Get(KeyType aKey) const
Get the value, returning a default-initialized object if the entry is
not present in the table.
.. cpp:function:: Maybe<V> MaybeGet(KeyType aKey) const
Get the value, returning Nothing if the entry is not present in the table.
.. cpp:function:: V& LookupOrInsert(KeyType aKey, Args&&... aArgs) const
.. cpp:function:: V& LookupOrInsertWith(KeyType aKey, F&& aFunc) const
.. cpp:class:: template<K> nsTHashSet<K>
The ``nsTHashSet<K>`` class is currently defined as a thin type alias
around ``nsTBaseHashSet``. See the methods defined on that class for
more detailed documentation.