[LyX/master] Some code factorization for the Change template

[Jean-Marc Lasgouttes]

commit f07ffaee84cef2b28c9d49e388d30f1f8e22cfc5
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Thu Mar 5 16:30:22 2015 +0100

    Some code factorization for the Change template
    
    The original motivation is to initialize the change_ member but do it only 
once.
    
    This fixes coverity issue 23432.

diff --git a/src/MetricsInfo.cpp b/src/MetricsInfo.cpp
index e68c18d..b75ec81 100644
--- a/src/MetricsInfo.cpp
+++ b/src/MetricsInfo.cpp
@@ -186,9 +186,8 @@ ArrayChanger::ArrayChanger(MetricsBase & mb)
 /////////////////////////////////////////////////////////////////////////
 
 ShapeChanger::ShapeChanger(FontInfo & font, FontShape shape)
-       : Changer<FontInfo, FontShape>(font)
+       : Changer<FontInfo, FontShape>(font, font.shape())
 {
-       save_ = orig_.shape();
        orig_.setShape(shape);
 }
 
@@ -213,7 +212,6 @@ StyleChanger::StyleChanger(MetricsBase & mb, Styles style)
                  { 0, 0, -3, -5 },
                  { 3, 3,  0, -2 },
                  { 5, 5,  2,  0 } };
-       save_ = mb;
        int t = diff[mb.style][style];
        if (t > 0)
                while (t--)
@@ -242,7 +240,6 @@ FontSetChanger::FontSetChanger(MetricsBase & mb, char const 
* name,
        : Changer<MetricsBase>(mb), change_(really_change_font)
 {
        if (change_) {
-               save_ = mb;
                FontSize oldsize = save_.font.size();
                ColorCode oldcolor = save_.font.color();
                docstring const oldname = from_ascii(save_.fontname);
@@ -263,7 +260,6 @@ FontSetChanger::FontSetChanger(MetricsBase & mb, docstring 
const & name,
        : Changer<MetricsBase>(mb), change_(really_change_font)
 {
        if (change_) {
-               save_ = mb;
                FontSize oldsize = save_.font.size();
                ColorCode oldcolor = save_.font.color();
                docstring const oldname = from_ascii(save_.fontname);
@@ -295,7 +291,6 @@ FontSetChanger::~FontSetChanger()
 WidthChanger::WidthChanger(MetricsBase & mb, int w)
        : Changer<MetricsBase>(mb)
 {
-       save_ = mb;
        mb.textwidth = w;
 }
 
@@ -314,10 +309,9 @@ WidthChanger::~WidthChanger()
 
 ColorChanger::ColorChanger(FontInfo & font, ColorCode color,
                           bool really_change_color)
-       : Changer<FontInfo, ColorCode>(font), change_(really_change_color)
+       : Changer<FontInfo, ColorCode>(font, font.color()), 
change_(really_change_color)
 {
        if (change_) {
-               save_ = font.color();
                font.setColor(color);
        }
 }
diff --git a/src/MetricsInfo.h b/src/MetricsInfo.h
index 05acbbb..88dd39f 100644
--- a/src/MetricsInfo.h
+++ b/src/MetricsInfo.h
@@ -126,15 +126,17 @@ public:
 class TextMetricsInfo {};
 
 
-/// Generic base for temporarily changing things.
-/// The original state gets restored when the Changer is destructed.
+/// Generic base for temporarily changing things. The derived class is
+/// responsible for restoring the original state when the Changer is
+/// destructed.
 template <class Struct, class Temp = Struct>
 class Changer {
-public:
-       ///
-       Changer(Struct & orig) : orig_(orig) {}
 protected:
        ///
+       Changer(Struct & orig, Temp const & save) : orig_(orig), save_(save) {}
+       ///
+       Changer(Struct & orig) : orig_(orig), save_(orig) {}
+       ///
        Struct & orig_;
        ///
        Temp save_;