Improve Map|Map-Reduce and Filter|Filter-Reduce implementation

* support lambda expressions
* remove the need to specify result_type
* use std::invoke to apply map|filter function
* remove usage of FunctionWrapper* and createFunctionWrapper

Task-number: QTBUG-33735
Task-number: QTBUG-82646
Change-Id: Ibcbe4278f0742c29182bd506081db0abb516f85f
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

1 files changed, 21 insertions, 2 deletions

diff --git a/src/concurrent/qtconcurrentfilter.cpp b/src/concurrent/qtconcurrentfilter.cpp
index bac8ac59fc..789188911e 100644
--- a/src/concurrent/qtconcurrentfilter.cpp
+++ b/src/concurrent/qtconcurrentfilter.cpp
@@ -144,8 +144,7 @@
     QtConcurrent::filter(), QtConcurrent::filtered(), and
     QtConcurrent::filteredReduced() accept function objects
     for the filter function. These function objects can be used to
-    add state to a function call. The result_type typedef must define the
-    result type of the function call operator:
+    add state to a function call:
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 13
 
@@ -155,6 +154,26 @@
 
     \snippet code/src_concurrent_qtconcurrentfilter.cpp 14
 
+    \section2 Using Lambda Expressions
+
+    QtConcurrent::filter(), QtConcurrent::filtered(), and
+    QtConcurrent::filteredReduced() accept lambda expressions for the filter and
+    reduce function:
+
+    \snippet code/src_concurrent_qtconcurrentfilter.cpp 15
+
+    When using QtConcurrent::filteredReduced() or
+    QtConcurrent::blockingFilteredReduced(), you can mix the use of normal
+    functions, member functions and lambda expressions freely.
+
+    \snippet code/src_concurrent_qtconcurrentfilter.cpp 16
+
+    For the reduce function, lambda expressions are not directly supported.
+    Lambda expressions can, however, be used when the type of the reduction
+    result is explicitly specified:
+
+    \snippet code/src_concurrent_qtconcurrentfilter.cpp 17
+
     \section2 Wrapping Functions that Take Multiple Arguments
 
     If you want to use a filter function takes more than one argument, you can