Add optional section about value type references

SlideDeck.qml

@@ -85,7 +85,7 @@ Presentation
     }
 
     Slide {
-        centeredText: "<b>Named value types</b><br>Containers of value types"
+        centeredText: "<b>Value types</b><br>Named value types<br>Containers of value types"
     }
 
     Slide {
@@ -106,7 +106,7 @@ Presentation
         title: "Value types"
         content: [
             "are generally <b>passed by value</b>",
-            " but still act like objects in JavaScript",
+            " but still act like objects in JavaScript (value type references!)",
             " common subset of object-like and value-like operations is compiled to C++",
             "need to be <b>default-constructible</b> and <b>copyable</b>",
             " are implicitly created and copied often",
@@ -117,6 +117,10 @@ Presentation
         ]
     }
 
+    Slide {
+        centeredText: "Value types<br><b>Named value types</b><br>Containers of value types"
+    }
+
     Slide {
         title: "Precondition: Follow best practices"
         content: [
@@ -277,7 +281,7 @@ Item {
     }
 
     Slide {
-        centeredText: "Named value types<br><b>Containers of value types</b>"
+        centeredText: "Value types<br>Named value types<br><b>Containers of value types</b>"
     }
 
     Slide {
@@ -508,4 +512,130 @@ Column {
         ]
     }
 
+    Slide {
+        title: "Value type references"
+
+        contentWidth: width / 2
+        content: [
+            "What does this program print?"
+        ]
+
+        QmlCodeSection {
+            text:
+`import QtQuick
+Text {
+    font {
+        pixelSize: 24
+        bold: false
+    }
+
+    function evil(f: font) : font {
+        font.pixelSize = 12
+        return f
+    }
+
+    Component.onCompleted: {
+        var f = font
+        var g = evil(f);
+        g.bold = true
+        console.log(font.bold, f.bold, g.bold)
+        console.log(font.pixelSize, f.pixelSize,
+                    g.pixelSize)
+    }
+}`
+        }
+    }
+
+    Slide {
+        title: "Value type references"
+
+        contentWidth: width / 2
+        content: [
+            "What does this program print?",
+            " true true true",
+            " 12 12 12",
+            "Wat?!",
+            " In JavaScript everything is an object",
+            " You cannot store a <b>font</b> on the stack",
+            " You cannot pass a <b>font</b> as value",
+            " Therefore, <b>value type references</b>",
+        ]
+
+        QmlCodeSection {
+            text:
+`import QtQuick
+Text {
+    font {
+        pixelSize: 24
+        bold: false
+    }
+
+    function evil(f: font) : font {
+        font.pixelSize = 12
+        return f
+    }
+
+    Component.onCompleted: {
+        var f = font
+        var g = evil(f);
+        g.bold = true
+        console.log(font.bold, f.bold, g.bold)
+        console.log(font.pixelSize, f.pixelSize,
+                    g.pixelSize)
+    }
+}`
+        }
+    }
+
+    Slide {
+        title: "Value type references"
+
+        contentWidth: width / 2
+        content: [
+            "In JavaScript everything is an object",
+            "<b>f</b> and <b>g</b> are <b>value type references</b>",
+            " Act as if font was an object",
+            " <b>Write back</b> any modification into <b>font</b>",
+            " <b>Read back</b> any modification from <b>font</b>",
+            " Magic! Aw...esome?...ful? Naughty!"
+        ]
+
+        QmlCodeSection {
+            text:
+`import QtQuick
+Text {
+    font {
+        pixelSize: 24
+        bold: false
+    }
+
+    function evil(f: font) : font {
+        font.pixelSize = 12
+        return f
+    }
+
+    Component.onCompleted: {
+        var f = font
+        var g = evil(f);
+        g.bold = true
+        console.log(font.bold, f.bold, g.bold)
+        console.log(font.pixelSize, f.pixelSize,
+                    g.pixelSize)
+    }
+}`
+        }
+    }
+
+    Slide {
+        title: "Value type references: safe subset"
+        content: [
+            "Only change value types in the statement that retrieves them",
+            "Pass value types only to pure functions",
+            "Explicitly re-load any value type references",
+            " after changing any property",
+            " after calling any impure function",
+            "Result: most of your QML code will be compiled to C++.",
+            "Except: qmlcachegen cannot identify pure functions, yet."
+        ]
+    }
 }