[poincare] Add Hierarchy::detachOperand to detach a single operand

poincare/include/poincare/hierarchy.h

@@ -11,8 +11,11 @@ public:
   const Expression * operand(int i) const override;
   void swapOperands(int i, int j) override;
   void replaceOperand(const Expression * oldOperand, Expression * newOperand, bool deleteOldOperand = true) override;
+  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;
+private:
+  void detachOperandAtIndex(int i);
 };
 
 }

poincare/src/hierarchy.cpp

@@ -21,14 +21,17 @@ void Hierarchy::swapOperands(int i, int j) {
   op[j] = temp;
 }
 
-void Hierarchy::detachOperands() {
-  Expression ** op = const_cast<Expression **>(operands());
+void Hierarchy::detachOperand(const Expression * e) {
   for (int i=0; i<numberOfOperands(); i++) {
-    // When detachOperands is called, it's very likely that said operands have been stolen
-    if (op[i]->parent() == this) {
-      const_cast<Expression *>(op[i])->setParent(nullptr);
+    if (operand(i) == e) {
+      detachOperandAtIndex(i);
     }
-    op[i] = nullptr;
+  }
+}
+
+void Hierarchy::detachOperands() {
+  for (int i=0; i<numberOfOperands(); i++) {
+    detachOperandAtIndex(i);
   }
 }
 
@@ -51,4 +54,13 @@ void Hierarchy::replaceOperand(const Expression * oldOperand, Expression * newOp
   }
 }
 
+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
+  if (op[i]->parent() == this) {
+    const_cast<Expression *>(op[i])->setParent(nullptr);
+  }
+  op[i] = nullptr;
+}
+
 }