[gtkmm] Gtk::PaperSize: Throw exception from a constructor

[Kjell Ahlstedt <kjellahl src gnome org>]

commit d868182595f5e791400f13c0faf16f0eabf51453
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Jul 11 10:25:01 2017 +0200

    Gtk::PaperSize: Throw exception from a constructor
    
    The constructor that reads from a Glib::KeyFile can fail. If it does,
    throw an exception instead of creating an invalid PaperSize instance.

 gtk/src/papersize.ccg |   13 ++++++++-----
 gtk/src/papersize.hg  |    8 ++++++++
 2 files changed, 16 insertions(+), 5 deletions(-)
---
diff --git a/gtk/src/papersize.ccg b/gtk/src/papersize.ccg
index 9cd04fd..f157fd0 100644
--- a/gtk/src/papersize.ccg
+++ b/gtk/src/papersize.ccg
@@ -57,12 +57,15 @@ PaperSize::PaperSize(const Glib::ustring& name, const Glib::ustring& display_nam
                                      GtkUnit(unit)))
 {}
 
-//TODO: Add an operator bool() so we can detect if this succeeded:
-//TODO: No, throw the error/exception instead.
 PaperSize::PaperSize(const Glib::KeyFile& key_file, const Glib::ustring& group_name)
-:
-  gobject_(gtk_paper_size_new_from_key_file(const_cast<GKeyFile*>(key_file.gobj()), (group_name.empty() ? 
nullptr : group_name.c_str()) , nullptr /* GError */))
-{}
+{
+  GError* gerror = nullptr;
+  gobject_ = gtk_paper_size_new_from_key_file(const_cast<GKeyFile*>(key_file.gobj()),
+    Glib::c_str_or_nullptr(group_name), &gerror);
+
+  if (gerror)
+    Glib::Error::throw_exception(gerror);
+}
 
 bool PaperSize::equal(const PaperSize& other) const
 {
diff --git a/gtk/src/papersize.hg b/gtk/src/papersize.hg
index db20a95..d423213 100644
--- a/gtk/src/papersize.hg
+++ b/gtk/src/papersize.hg
@@ -63,6 +63,14 @@ public:
   explicit PaperSize(const Glib::ustring& ppd_name, const Glib::ustring& ppd_display_name, double width, 
double height);
   explicit PaperSize(const Glib::ustring& name, const Glib::ustring& display_name, double width, double 
height, Unit unit);
 
+  /** Reads a paper size from the group @a group_name in the key file @a key_file.
+   *
+   * @param key_file The Glib::KeyFile to retrieve the paper size from.
+   * @param group_name The name of the group in the key file to read,
+   *                   or an empty string to read the first group.
+   *
+   * @throws Gtk::PrintError, Glib::KeyFileError
+   */
   explicit PaperSize(const Glib::KeyFile& key_file, const Glib::ustring& group_name = Glib::ustring());
 
   _IGNORE(gtk_paper_size_copy, gtk_paper_size_free, gtk_paper_size_is_equal)