Refactor mapping to the native structs

imgui-binding/src/main/java/imgui/binding/ImGuiStruct.java

@@ -0,0 +1,18 @@
+package imgui.binding;
+
+import imgui.ImGui;
+
+/**
+ * Class provides a communication layer between binding and Dear ImGui library though the "pointer" field.
+ */
+public abstract class ImGuiStruct {
+    /**
+     * Pointer to the natively allocated object,
+     */
+    public long ptr;
+
+    public ImGuiStruct(final long ptr) {
+        ImGui.touch();
+        this.ptr = ptr;
+    }
+}

imgui-binding/src/main/java/imgui/binding/ImGuiStructDestroyable.java

@@ -0,0 +1,31 @@
+package imgui.binding;
+
+/**
+ * Class extends {@link ImGuiStruct} and provides additional API to allocated and de-allocate native objects.
+ */
+public abstract class ImGuiStructDestroyable extends ImGuiStruct {
+    /**
+     * Constructor, which creates natively allocated struct. Those structs should be manually disposed with {@link #destroy()} method.
+     */
+    public ImGuiStructDestroyable() {
+        this(0);
+        ptr = create();
+    }
+
+    public ImGuiStructDestroyable(final long ptr) {
+        super(ptr);
+    }
+
+    protected abstract long create();
+
+    /**
+     * Method to free natively allocated memory for the struct mapped with pointer.
+     */
+    public void destroy() {
+        nDestroy(ptr);
+    }
+
+    private native void nDestroy(long ptr); /*
+        delete (void*)ptr;
+    */
+}