UI-Coordinates: support for truncating a given spec

...implemented within the builder.
Will shorten and discard extraneous storage,
but not expand and allocate new one

src/gui/interact/ui-coord.hpp

@@ -583,6 +583,14 @@ namespace interact {
           uic_.setTailSequence (UIC_PATH, pathDef);
           return std::move (*this);
         }
+
+      /** possibly shorten this path specification to a limited depth */
+      Builder
+      truncateTo (size_t depth)
+        {
+          uic_.truncateTo (depth);
+          return std::move (*this);
+        }
     };
   
   

src/lib/path-array.hpp

@@ -477,6 +477,23 @@ namespace lib {
           *reinterpret_cast<const char**> (pos) = val;
         }
       
+      void
+      truncateTo (size_t newSize)
+        {
+          if (newSize < chunk_size)
+            {
+              Literal* end = elms_.end();
+              Literal* pos = getPosition(newSize);
+              for ( ; pos!=end; ++pos)
+                setContent (pos, nullptr);
+              tail_.resizeTo (0);
+            }
+          else
+            if (newSize-chunk_size < tail_.size())
+              tail_.resizeTo (newSize - chunk_size);
+            // otherwise: keep current size, don't grow
+        }
+      
       /**
        * establish the _contract_ of PathArray
        * - no null pointer within the valid storage range

tests/gui/interact/ui-coord-test.cpp

@@ -189,6 +189,17 @@ namespace test {
           CHECK (5 == uic4.size());
           CHECK ("UI:?-panel.view.#555" == string(uic4));
           VERIFY_ERROR(LOGIC, uic1.prepend("root"));
+          
+          // the builder may shorten/truncate the path
+          uic4 = uic4.append("α/β/γ/δ/ε/λ").truncateTo(9);
+          CHECK (9 == uic4.size());
+          CHECK ("UI:?-panel.view.#555/α/β/γ/δ" == string(uic4));
+          uic4 = uic4.path("ε/ε/ε/ε/ε").truncateTo(3);
+          CHECK (3 == uic4.size());
+          CHECK ("UI:?-panel" == string(uic4));
+          uic4 = uic4.append("something").truncateTo(2);
+          CHECK (0 == uic4.size());    // NOTE: normalisation detected absence of any remaining content
+          CHECK ("UI:?" == string(uic4));
         }
       
       

tests/library/path-array-test.cpp

@@ -451,6 +451,10 @@ namespace test {
           CHECK ("" == parr[4]);
           CHECK ("" == parr[5]);
           CHECK ("Φ" == parr[6]);
+          
+          parr = ParrT{"",nullptr,"",nullptr,"",nullptr,""};
+          CHECK ("" == join(parr,""));
+          CHECK (0 == parr.size());
         }