make conversions away from NR::Maybe explicit

(bzr r2530)

7 files changed, 32 insertions, 52 deletions

diff --git a/src/event-context.cpp b/src/event-context.cpp
index 0cf4f8924..7a3de5e85 100644
--- a/src/event-context.cpp
+++ b/src/event-context.cpp
@@ -463,8 +463,8 @@ static gint sp_event_context_private_root_handler(SPEventContext *event_context,
                 zoom_rb = 0;
                 NR::Maybe<NR::Rect> const b = Inkscape::Rubberband::get()->getRectangle();
                 Inkscape::Rubberband::get()->stop();
-                if (b != NR::Nothing() && !within_tolerance) {
-                    desktop->set_display_area(b.assume(), 10);
+                if (b && !within_tolerance) {
+                    desktop->set_display_area(*b, 10);
                 }
                 ret = TRUE;
             }
diff --git a/src/libnr/nr-maybe.h b/src/libnr/nr-maybe.h
index 6eed01ec1..9c1aa0708 100644
--- a/src/libnr/nr-maybe.h
+++ b/src/libnr/nr-maybe.h
@@ -29,27 +29,7 @@ public:
     IsNot() : domain_error(std::string("Is not ") + typeid(T).name()) {}
 };
 
-/** A type with only one value, which (in principle) is only equal to itself.
- *
- *  Types that may (at runtime) pretend to be Nothing need only provide an
- *  operator bool operator==(Type, Nothing); the rest of the operator
- *  definitions will be taken care of automatically.
- *
- *  Such types should also provide a casting operator to Nothing, obviously.
- */
-struct Nothing {
-    bool operator==(Nothing n) { return true; }
-    bool operator!=(Nothing n) { return false; }
-    template <typename T>
-    bool operator==(T t) { return t == *this; }
-    template <typename T>
-    bool operator!=(T t) { return t != *this; }
-};
-
-template <typename T>
-bool operator==(T t, Nothing n) { return false; }
-template <typename T>
-bool operator!=(T t, Nothing n) { return !( t == n ); }
+struct Nothing {};
 
 template <typename T>
 struct MaybeTraits;
@@ -59,6 +39,7 @@ class Maybe {
 public:
     typedef MaybeTraits<T> traits;
     typedef typename traits::storage storage;
+    typedef typename traits::pointer pointer;
     typedef typename traits::reference reference;
 
     Maybe(Nothing n) : _is_nothing(true), _t() {}
@@ -73,32 +54,21 @@ public:
     template <typename T2>
     Maybe(T2 t) : _is_nothing(false), _t(traits::to_storage(t)) {}
 
-    reference assume() const throw(IsNot<T>) {
-        if (_is_nothing) {
-            throw IsNot<T>();
-        } else {
-            return traits::from_storage(_t);
-        }
-    }
+    bool isNothing() const { return _is_nothing; }
+    operator bool() const { return !_is_nothing; }
 
-    operator reference() const throw(IsNot<T>) {
+    reference assume() const throw(IsNot<T>) {
         if (_is_nothing) {
             throw IsNot<T>();
         } else {
             return traits::from_storage(_t);
         }
     }
-    operator Nothing() const throw(IsNot<Nothing>) {
-        if (!_is_nothing) {
-            throw IsNot<Nothing>();
-        } else {
-            return Nothing();
-        }
+    reference operator*() const throw(IsNot<T>) {
+        return assume();
     }
-
-    bool operator==(Nothing n) { return _is_nothing; }
-    bool operator==(reference r) {
-        return traits::from_storage(_t) == r;
+    pointer operator->() const throw(IsNot<T>) {
+        return &assume();
     }
 
 private:
@@ -111,6 +81,7 @@ private:
 template <typename T>
 struct MaybeTraits {
     typedef T const storage;
+    typedef T const *pointer;
     typedef T const &reference;
     static reference to_storage(reference t) { return t; }
     static reference from_storage(reference t) { return t; }
@@ -119,6 +90,7 @@ struct MaybeTraits {
 template <typename T>
 struct MaybeTraits<T&> {
     typedef T *storage;
+    typedef T *pointer;
     typedef T &reference;
     static storage to_storage(reference t) { return &t; }
     static reference from_storage(storage t) { return *t; }
diff --git a/src/node-context.cpp b/src/node-context.cpp
index 235b89db3..352bac584 100644
--- a/src/node-context.cpp
+++ b/src/node-context.cpp
@@ -419,8 +419,8 @@ sp_node_context_root_handler(SPEventContext *event_context, GdkEvent *event)
 
                 if (nc->shape_editor->hits_curve() && !event_context->within_tolerance) { //drag curve
                     nc->shape_editor->finish_drag();
-                } else if (b != NR::Nothing() && !event_context->within_tolerance) { // drag to select
-                    nc->shape_editor->select_rect(b.assume(), event->button.state & GDK_SHIFT_MASK);
+                } else if (b && !event_context->within_tolerance) { // drag to select
+                    nc->shape_editor->select_rect(*b, event->button.state & GDK_SHIFT_MASK);
                 } else {
                     if (!(nc->rb_escaped)) { // unless something was cancelled
                         if (nc->shape_editor->has_selection())
@@ -584,7 +584,7 @@ sp_node_context_root_handler(SPEventContext *event_context, GdkEvent *event)
                 case GDK_Escape:
                 {
                     NR::Maybe<NR::Rect> const b = Inkscape::Rubberband::get()->getRectangle();
-                    if (b != NR::Nothing()) {
+                    if (b) {
                         Inkscape::Rubberband::get()->stop();
                         nc->current_state = SP_NODE_CONTEXT_INACTIVE;
                         nc->rb_escaped = true;
diff --git a/src/nodepath.cpp b/src/nodepath.cpp
index 78d76404d..1d854418b 100644
--- a/src/nodepath.cpp
+++ b/src/nodepath.cpp
@@ -1549,7 +1549,11 @@ sp_nodepath_select_segment_near_point(Inkscape::NodePath::Path *nodepath, NR::Po
     }
 
     sp_nodepath_ensure_livarot_path(nodepath);
-    Path::cut_position position = get_nearest_position_on_Path(nodepath->livarot_path, p);
+    NR::Maybe<Path::cut_position> maybe_position = get_nearest_position_on_Path(nodepath->livarot_path, p);
+    if (!maybe_position) {
+        return;
+    }
+    Path::cut_position position = *maybe_position;
 
     //find segment to segment
     Inkscape::NodePath::Node *e = sp_nodepath_get_node_by_index(position.piece);
@@ -1581,7 +1585,11 @@ sp_nodepath_add_node_near_point(Inkscape::NodePath::Path *nodepath, NR::Point p)
     }
 
     sp_nodepath_ensure_livarot_path(nodepath);
-    Path::cut_position position = get_nearest_position_on_Path(nodepath->livarot_path, p);
+    NR::Maybe<Path::cut_position> maybe_position = get_nearest_position_on_Path(nodepath->livarot_path, p);
+    if (!maybe_position) {
+        return;
+    }
+    Path::cut_position position = *maybe_position;
 
     //find segment to split
     Inkscape::NodePath::Node *e = sp_nodepath_get_node_by_index(position.piece);
diff --git a/src/object-snapper.cpp b/src/object-snapper.cpp
index 6b51f8508..4a21cbc04 100644
--- a/src/object-snapper.cpp
+++ b/src/object-snapper.cpp
@@ -128,7 +128,7 @@ void Inkscape::ObjectSnapper::_snapPaths(Inkscape::SnappedPoint &s,
 
         /* Look for the nearest position on this SPItem to our snap point */
         NR::Maybe<Path::cut_position> const o = get_nearest_position_on_Path(livarot_path, p_it);
-        if (o != NR::Nothing() && o.assume().t >= 0 && o.assume().t <= 1) {
+        if (o && o->t >= 0 && o->t <= 1) {
 
             /* Convert the nearest point back to desktop coordinates */
             NR::Point const o_it = get_point_on_Path(livarot_path, o.assume().piece, o.assume().t);
diff --git a/src/select-context.cpp b/src/select-context.cpp
index 5d8babe57..e1649e34f 100644
--- a/src/select-context.cpp
+++ b/src/select-context.cpp
@@ -229,7 +229,7 @@ sp_select_context_abort(SPEventContext *event_context)
         }
     } else {
         NR::Maybe<NR::Rect> const b = Inkscape::Rubberband::get()->getRectangle();
-        if (b != NR::Nothing()) {
+        if (b) {
             Inkscape::Rubberband::get()->stop();
             rb_escaped = 1;
             SP_EVENT_CONTEXT(sc)->desktop->messageStack()->flash(Inkscape::NORMAL_MESSAGE, _("Selection canceled."));
@@ -567,12 +567,12 @@ sp_select_context_root_handler(SPEventContext *event_context, GdkEvent *event)
                     sc->item = NULL;
                 } else {
                     NR::Maybe<NR::Rect> const b = Inkscape::Rubberband::get()->getRectangle();
-                    if (b != NR::Nothing() && !within_tolerance) {
+                    if (b && !within_tolerance) {
                         // this was a rubberband drag
                         Inkscape::Rubberband::get()->stop();
                         seltrans->resetState();
                         // find out affected items:
-                        GSList *items = sp_document_items_in_box(sp_desktop_document(desktop), desktop->dkey, b.assume());
+                        GSList *items = sp_document_items_in_box(sp_desktop_document(desktop), desktop->dkey, *b);
                         if (event->button.state & GDK_SHIFT_MASK) {
                             // with shift, add to selection
                             selection->addList (items);
diff --git a/src/zoom-context.cpp b/src/zoom-context.cpp
index 62395581f..d2b0d6849 100644
--- a/src/zoom-context.cpp
+++ b/src/zoom-context.cpp
@@ -163,8 +163,8 @@ static gint sp_zoom_context_root_handler(SPEventContext *event_context, GdkEvent
 	case GDK_BUTTON_RELEASE:
             if ( event->button.button == 1 ) {
                 NR::Maybe<NR::Rect> const b = Inkscape::Rubberband::get()->getRectangle();
-                if (b != NR::Nothing() && !within_tolerance) {
-                    desktop->set_display_area(b.assume(), 10);
+                if (b && !within_tolerance) {
+                    desktop->set_display_area(*b, 10);
                 } else if (!escaped) {
                     NR::Point const button_w(event->button.x, event->button.y);
                     NR::Point const button_dt(desktop->w2d(button_w));