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-rw-r--r--src/corelib/doc/src/containers.qdoc73
1 files changed, 10 insertions, 63 deletions
diff --git a/src/corelib/doc/src/containers.qdoc b/src/corelib/doc/src/containers.qdoc
index 4a5de26f14..c5b70c2675 100644
--- a/src/corelib/doc/src/containers.qdoc
+++ b/src/corelib/doc/src/containers.qdoc
@@ -61,9 +61,6 @@
STL's \l{generic algorithms}.
\l{Java-style Iterators} are provided for backwards compatibility.
- Qt also offers a \l{foreach} keyword that make it very
- easy to iterate over all the items stored in a container.
-
\note Since Qt 5.14, range constructors are available for most of the
container classes. QMultiMap is a notable exception. Their use is
encouraged in place of the various from/to methods. For example:
@@ -360,68 +357,15 @@
on Java's iterator classes.
New code should should prefer \l{STL-Style Iterators}.
- \target foreach
- \section1 The foreach Keyword
-
- If you just want to iterate over all the items in a container
- in order, you can use Qt's \c foreach keyword. The keyword is a
- Qt-specific addition to the C++ language, and is implemented
- using the preprocessor.
-
- Its syntax is: \c foreach (\e variable, \e container) \e
- statement. For example, here's how to use \c foreach to iterate
- over a QList<QString>:
-
- \snippet code/doc_src_containers.cpp 15
-
- The \c foreach code is significantly shorter than the equivalent
- code that uses iterators:
-
- \snippet code/doc_src_containers.cpp 16
-
- Unless the data type contains a comma (e.g., \c{QPair<int,
- int>}), the variable used for iteration can be defined within the
- \c foreach statement:
-
- \snippet code/doc_src_containers.cpp 17
-
- And like any other C++ loop construct, you can use braces around
- the body of a \c foreach loop, and you can use \c break to leave
- the loop:
+ \section1 Container keywords
- \snippet code/doc_src_containers.cpp 18
-
- With QMap and QHash, \c foreach accesses the value component of
- the (key, value) pairs automatically, so you should not call
- values() on the container (it would generate an unnecessary copy,
- see below). If you want to iterate over both the keys and the
- values, you can use iterators (which are faster), or you can
- obtain the keys, and use them to get the values too:
-
- \snippet code/doc_src_containers.cpp 19
-
- For a multi-valued map:
-
- \snippet code/doc_src_containers.cpp 20
-
- Qt automatically takes a copy of the container when it enters a
- \c foreach loop. If you modify the container as you are
- iterating, that won't affect the loop. (If you do not modify the
- container, the copy still takes place, but thanks to \l{implicit
- sharing} copying a container is very fast.)
-
- Since foreach creates a copy of the container, using a non-const
- reference for the variable does not allow you to modify the original
- container. It only affects the copy, which is probably not what you
- want.
-
- An alternative to Qt's \c foreach loop is the range-based \c for that is
- part of C++ 11 and newer. However, keep in mind that the range-based
- \c for might force a Qt container to \l{Implicit Sharing}{detach}, whereas
- \c foreach would not. But using \c foreach always copies the container,
- which is usually not cheap for STL containers. If in doubt, prefer
- \c foreach for Qt containers, and range based \c for for STL ones.
+ \target foreach
+ \section2 The foreach Keyword
+ \l{foreach-keyword}{The foreach keyword} is discouraged, new code should
+ prefer C++11 range-based loops.
+ \target forever
+ \section2 The forever keyword.
In addition to \c foreach, Qt also provides a \c forever
pseudo-keyword for infinite loops:
@@ -432,6 +376,9 @@
\snippet code/doc_src_containers.cpp 22
+ \note The alternative macros Q_FOREACH and Q_FOREVER remain defined
+ regardless.
+
\section1 Other Container-Like Classes
Qt includes other template classes that resemble containers in