editor: add 'line_kill'

This also adds nullptr checking to decref--it seemed the functions
needing nullptr checks immediately prior to the decref call was
beginning to exceed the functions that had "implied" nullptr checking
as a part of their natural flow-control.

editor/editor.hpp

@@ -101,6 +101,7 @@ struct buffer {
   inline constexpr void cursor_scan_word_backward();
 
   inline constexpr bool enter();
+  inline constexpr void line_kill();
   inline constexpr void mark_set();
   inline constexpr selection mark_get();
   inline constexpr void delete_from_line(line<C> *& l,
@@ -180,7 +181,8 @@ inline constexpr void buffer<C, R>::deallocate(line<C> *& l)
 template <int C, int R>
 inline constexpr void buffer<C, R>::decref(line<C> *& l)
 {
-  if (l->refcount == 1)
+  if (l == nullptr) return;
+  else if (l->refcount == 1)
     buffer<C, R>::deallocate(l);
   else {
     l->refcount--;
@@ -585,6 +587,27 @@ inline constexpr bool buffer<C, R>::enter()
   return true;
 }
 
+template <int C, int R>
+inline constexpr void buffer<C, R>::line_kill()
+{
+  editor::cursor& cur = this->cursor;
+
+  if (line_length(this->lines[cur.row]) == 0) {
+    decref(this->lines[cur.row]);
+
+    // shift all lines up by one
+    int32_t n_lines = this->length - (cur.row + 1);
+    move(&this->lines[cur.row],
+	 &this->lines[cur.row+1],
+	 (sizeof (line<C>*)) * n_lines);
+    this->length--;
+    this->lines[this->length] = nullptr;
+  } else {
+    line<C> * l = mutref(this->lines[cur.row]);
+    l->length = cur.col;
+  }
+}
+
 template <int C, int R>
 inline constexpr void buffer<C, R>::mark_set()
 {
@@ -719,7 +742,6 @@ template <int C, int R>
 inline constexpr void buffer<C, R>::shadow_clear()
 {
   for (int32_t i = 0; i < this->shadow.length; i++)
-    if (this->shadow.lines[i] != nullptr)
     decref(this->shadow.lines[i]);
 
   this->shadow.length = 1;
@@ -815,7 +837,7 @@ inline constexpr void buffer<C, R>::overwrite_line(line<C> *& dst,
     //else do nothing
   } else if (dst_col == 0 && src_col == 0 &&
 	     line_length(src) >= line_length(dst)) {
-    if (dst != nullptr) decref(dst);
+    decref(dst);
     dst = incref(src);
   } else {
     line<C> * dstmut = mutref(dst);

editor/main_saturn.cpp

@@ -139,6 +139,7 @@ inline void keyboard_regular_key(const enum keysym k)
     case keysym::E        : buffer.cursor_end(); break;
     case keysym::Y        : buffer.shadow_paste(); break;
     case keysym::W        : buffer.shadow_cut(); break;
+    case keysym::K        : buffer.line_kill(); break;
     default: break;
     }
     break;