diff options
| -rw-r--r-- | src/corelib/doc/src/containers.qdoc | 23 | ||||
| -rw-r--r-- | src/corelib/global/qglobal.cpp | 13 |
2 files changed, 33 insertions, 3 deletions
diff --git a/src/corelib/doc/src/containers.qdoc b/src/corelib/doc/src/containers.qdoc index 9cda3f91d8..4a5de26f14 100644 --- a/src/corelib/doc/src/containers.qdoc +++ b/src/corelib/doc/src/containers.qdoc @@ -527,6 +527,29 @@ with the expected number of items before you insert the items. The next section discusses this topic in more depth. + \section1 Optimizations for Primitive and Relocatable Types + + Qt containers can use optimized code paths if the stored + elements are relocatable or even primitive. + However, whether types are primitive or relocatable + cannot be detected in all cases. + You can declare your types to be primitive or relocatable + by using the Q_DECLARE_TYPEINFO macro with the Q_PRIMITIVE_TYPE + flag or the Q_RELOCATABLE_TYPE flag. See the documentation + of Q_DECLARE_TYPEINFO for further details and usage examples. + + If you do not use Q_DECLARE_TYPEINFO, + Qt will use + \l {https://en.cppreference.com/w/cpp/types/is_trivial} {std::is_trivial_v<T>} + to indentify primitive + types and it will require both + \l {https://en.cppreference.com/w/cpp/types/is_trivially_copyable} {std::is_trivially_copyable_v<T>} + and + \l {https://en.cppreference.com/w/cpp/types/is_destructible} {std::is_trivially_destructible_v<T>} + to identify relocatable types. + This is always a safe choice, albeit + of maybe suboptimal performance. + \section1 Growth Strategies QList<T>, QString, and QByteArray store their items diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp index 62ca2ca8a1..bcfc6ada2e 100644 --- a/src/corelib/global/qglobal.cpp +++ b/src/corelib/global/qglobal.cpp @@ -3995,12 +3995,19 @@ bool qunsetenv(const char *varName) pattern still represents a valid object, and memcpy() can be used to create a valid independent copy of a QUuid object. - Example of a movable type: + Example of a relocatable type: \snippet code/src_corelib_global_qglobal.cpp 39 - Qt will try to detect the class of a type using std::is_trivial or - std::is_trivially_copyable. Use this macro to tune the behavior. + Qt will try to detect the class of a type using + \l {https://en.cppreference.com/w/cpp/types/is_trivial} {std::is_trivial_v<T>} + to indentify primitive + types and it will require both + \l {https://en.cppreference.com/w/cpp/types/is_trivially_copyable} {std::is_trivially_copyable_v<T>} + and + \l {https://en.cppreference.com/w/cpp/types/is_destructible} {std::is_trivially_destructible_v<T>} + to identify relocatable types. + Use this macro to tune the behavior. For instance many types would be candidates for Q_RELOCATABLE_TYPE despite not being trivially-copyable. */ |