From 41046c0d4469e26114272737921d9601f9717882 Mon Sep 17 00:00:00 2001
From: hjk <hjk@qt.io>
Date: Thu, 18 Jul 2024 10:11:33 +0200
Subject: [PATCH] LayoutBuilder: Initialize BuilderItem::apply more directly

Also, add some timing information.

Change-Id: I5d38cac9e7ad0afb24504ff521f31d5202268462
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
---
 src/libs/utils/builderutils.h           | 12 ++++----
 tests/manual/layoutbuilder/v2/README.md | 37 +++++++++++++++++++++++++
 tests/manual/layoutbuilder/v2/lb.h      | 10 +++----
 3 files changed, 46 insertions(+), 13 deletions(-)
 create mode 100644 tests/manual/layoutbuilder/v2/README.md

diff --git a/src/libs/utils/builderutils.h b/src/libs/utils/builderutils.h
index ea5f747a3c9..5ab620bd06c 100644
--- a/src/libs/utils/builderutils.h
+++ b/src/libs/utils/builderutils.h
@@ -27,18 +27,16 @@ public:
     // Property setter
     template <typename Id, typename Arg>
     BuilderItem(IdAndArg<Id, Arg> && idarg)
-    {
-        apply = [&idarg](X *x) { doit(x, Id{}, idarg.arg); };
-    }
+        : apply([&idarg](X *x) { doit(x, Id{}, idarg.arg); })
+    {}
 
     // Nested child object
     template <typename Inner>
     BuilderItem(Inner && p)
-    {
-        apply = [&p](X *x) { doit(x, NestId{}, std::forward<Inner>(p)); };
-    }
+        : apply([&p](X *x) { doit(x, NestId{}, std::forward<Inner>(p)); })
+    {}
 
-    std::function<void(X *)> apply;
+    const std::function<void(X *)> apply;
 };
 
 #define QTC_DEFINE_BUILDER_SETTER(name, setter) \
diff --git a/tests/manual/layoutbuilder/v2/README.md b/tests/manual/layoutbuilder/v2/README.md
new file mode 100644
index 00000000000..d46aede5e0a
--- /dev/null
+++ b/tests/manual/layoutbuilder/v2/README.md
@@ -0,0 +1,37 @@
+
+This is an ad-hoc instruction count to judge the overhead imposed
+by Layoutbuilder for
+
+    Label ll {
+        text("World")
+    };
+
+
+(1) up to Label::Label
+(2) after new Label to up to doit()
+(3) tuple stuff in doit up to QLabel::setText parameter construction
+
+
+With
+
+    BuilderItem(IdAndArg<Id, Arg> && idarg)
+    {
+        apply = [&idarg](X *x) { doit(x, Id{}, idarg.arg); };
+    }
+
+
+    (1)   (2) + (3)    Sum
+-O0 547   259 + 802   1608
+-O2  24       23        47
+
+
+
+With
+
+    BuilderItem(IdAndArg<Id, Arg> && idarg)
+        : apply([&idarg](X *x) { doit(x, Id{}, idarg.arg); })
+    {}
+
+
+    (1)   (2) + (3)    Sum
+-O2  5        23        28
diff --git a/tests/manual/layoutbuilder/v2/lb.h b/tests/manual/layoutbuilder/v2/lb.h
index 2d92f168a1c..6248a4fcb36 100644
--- a/tests/manual/layoutbuilder/v2/lb.h
+++ b/tests/manual/layoutbuilder/v2/lb.h
@@ -61,16 +61,14 @@ public:
     // Property setter
     template <typename Id, typename Arg>
     BuilderItem(IdAndArg<Id, Arg> && idarg)
-    {
-        apply = [&idarg](X *x) { doit(x, Id{}, idarg.arg); };
-    }
+        : apply([&idarg](X *x) { doit(x, Id{}, idarg.arg); })
+    {}
 
     // Nested child object
     template <typename Inner>
     BuilderItem(Inner && p)
-    {
-        apply = [&p](X *x) { doit(x, NestId{}, std::forward<Inner>(p)); };
-    }
+        : apply([&p](X *x) { doit(x, NestId{}, std::forward<Inner>(p)); })
+    {}
 
     std::function<void(X *)> apply;
 };