path: root/tests/benchmarks/corelib/kernel
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authorKent Hansen <>2011-10-10 11:56:43 +0200
committerQt by Nokia <>2011-10-19 10:25:28 +0200
commit9e92ecde74d33eddd39de88472964fb20feaaebf (patch)
treec127c382451255cf64d6259c33dc34c754e965b8 /tests/benchmarks/corelib/kernel
parentae30d71413595b3cb0550e047132ea07510d35a3 (diff)
Provide API for "placement new" construction of meta-types
By making it possible to specify the place in memory where a type should be constructed, any meta-type can be allocated on the stack, for example. In the QML/JS QObject binding, this makes it possible to call slots and access properties from JavaScript without having to perform any mallocs (e.g. due to QVariant creation) in the C++ <--> JS value conversion, in the best case. In addition to QMetaType::construct() and QMetaType::destruct(), this change introduces QMetaType::typeSize(), which returns the size of a type in bytes. This can be used to prepare a suitable buffer for constructing a type using construct(). Benchmarks indicate that in-place construction is 2-5x faster than normal construction for core and GUI types on linux-g++. Note that there is already a QMetaType::construct() function in Qt 4, which has been renamed to QMetaType::create() in Qt 5. In order to avoid existing usages of construct() in user code to call the Qt 5 construct() (when they really meant to call create()), the third argument ("copy") of construct() is made mandatory. Hence, calls to QMetaType::construct() written for Qt 4 will cause a compile error when compiled with Qt 5, and the user must adapt his code. Task-number: QTBUG-12574 Change-Id: I836f06f6ee1c1c3edbd199a03424c78c942bdd3e Reviewed-by: João Abecasis <> Reviewed-by: Kent Hansen <>
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