[poincare] Add a shortcut constructor in Hierarchy

Change-Id: I2b0de8ab43ae6a0503814a48a20991b4c92572ea

poincare/include/poincare/dynamic_hierarchy.h

@@ -10,6 +10,8 @@ class DynamicHierarchy : public Hierarchy {
 public:
   DynamicHierarchy();
   DynamicHierarchy(const Expression * const * operands, int numberOfOperands, bool cloneOperands = true);
+  DynamicHierarchy(const Expression * operand1, const Expression * operand2, bool cloneOperands = true) :
+   DynamicHierarchy(ExpressionArray(operand1, operand2), 2, cloneOperands) {}
   ~DynamicHierarchy();
   DynamicHierarchy(const DynamicHierarchy & other) = delete;
   DynamicHierarchy(DynamicHierarchy && other) = delete;

poincare/include/poincare/hierarchy.h

@@ -14,6 +14,8 @@ public:
   void detachOperand(const Expression * e); // Removes an operand WITHOUT deleting it
   void detachOperands(); // Removes all operands WITHOUT deleting them
   virtual const Expression * const * operands() const = 0;
+protected:
+  static const Expression * const * ExpressionArray(const Expression * e1, const Expression * e2);
 private:
   void detachOperandAtIndex(int i);
 };

poincare/include/poincare/static_hierarchy.h

@@ -11,6 +11,7 @@ class StaticHierarchy : public Hierarchy {
 public:
   StaticHierarchy();
   StaticHierarchy(const Expression * const * operands, bool cloneOperands = true);
+  StaticHierarchy(const Expression * expression1, const Expression * expression2, bool cloneOperands = true); // Specialized constructor for StaticHierarchy<2>
   ~StaticHierarchy();
   StaticHierarchy(const StaticHierarchy & other) = delete;
   StaticHierarchy(StaticHierarchy && other) = delete;

poincare/src/hierarchy.cpp

@@ -59,6 +59,13 @@ void Hierarchy::replaceOperand(const Expression * oldOperand, Expression * newOp
   }
 }
 
+const Expression * const * Hierarchy::ExpressionArray(const Expression * e1, const Expression * e2) {
+  static const Expression * result[2] = {nullptr, nullptr};
+  result[0] = e1;
+  result[1] = e2;
+  return result;
+}
+
 void Hierarchy::detachOperandAtIndex(int i) {
   Expression ** op = const_cast<Expression **>(operands());
   // When detachOperands is called, it's very likely that said operands have been stolen

poincare/src/static_hierarchy.cpp

@@ -19,6 +19,12 @@ StaticHierarchy<T>::StaticHierarchy(const Expression * const * operands, bool cl
   build(operands, T, cloneOperands);
 }
 
+template<>
+StaticHierarchy<2>::StaticHierarchy(const Expression * e1, const Expression * e2, bool cloneOperands) :
+  StaticHierarchy(ExpressionArray(e1, e2), cloneOperands)
+{
+}
+
 template<int T>
 StaticHierarchy<T>::~StaticHierarchy() {
   for (int i = 0; i < T; i++) {