From 500025090f94a116ab8e0079a1aed41c0063ebf0 Mon Sep 17 00:00:00 2001
From: Ellpeck <megamaximal@gmail.com>
Date: Sun, 25 Oct 2020 20:11:15 +0100
Subject: [PATCH] added a CopyConstructor attribute to CopyExtensions

---
 MLEM.Data/CopyExtensions.cs | 25 +++++++++++++++++++------
 Sandbox/GameImpl.cs         | 11 ++++++++---
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/MLEM.Data/CopyExtensions.cs b/MLEM.Data/CopyExtensions.cs
index e621c05..1c2064f 100644
--- a/MLEM.Data/CopyExtensions.cs
+++ b/MLEM.Data/CopyExtensions.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Reflection;
 
 namespace MLEM.Data {
@@ -11,7 +12,7 @@ namespace MLEM.Data {
 
         /// <summary>
         /// Creates a shallow copy of the object and returns it.
-        /// Note that, for this to work correctly, <typeparamref name="T"/> needs to contain a parameterless constructor.
+        /// Note that, for this to work correctly, <typeparamref name="T"/> needs to contain a parameterless constructor or a constructor with the <see cref="CopyConstructorAttribute"/>.
         /// </summary>
         /// <param name="obj">The object to create a shallow copy of</param>
         /// <param name="flags">The binding flags for field searching</param>
@@ -26,7 +27,7 @@ namespace MLEM.Data {
 
         /// <summary>
         /// Creates a deep copy of the object and returns it.
-        /// Note that, for this to work correctly, <typeparamref name="T"/> needs to contain a parameterless constructor.
+        /// Note that, for this to work correctly, <typeparamref name="T"/> needs to contain a parameterless constructor or a constructor with the <see cref="CopyConstructorAttribute"/>.
         /// </summary>
         /// <param name="obj">The object to create a deep copy of</param>
         /// <param name="flags">The binding flags for field searching</param>
@@ -56,7 +57,7 @@ namespace MLEM.Data {
 
         /// <summary>
         /// Copies the given object <paramref name="obj"/> into the given object <paramref name="otherObj"/> in a deep manner.
-        /// Note that, for this to work correctly, each type that should be constructed below the topmost level needs to contanin a parameterless constructor.
+        /// Note that, for this to work correctly, each type that should be constructed below the topmost level needs to contanin a parameterless constructor or a constructor with the <see cref="CopyConstructorAttribute"/>.
         /// </summary>
         /// <param name="obj">The object to create a deep copy of</param>
         /// <param name="otherObj">The object to copy into</param>
@@ -84,11 +85,23 @@ namespace MLEM.Data {
         }
 
         private static object Construct(Type t, BindingFlags flags) {
-            var constructor = t.GetConstructor(flags, null, Type.EmptyTypes, null);
+            // find a contructor with the correct attribute
+            var constructor = t.GetConstructors().FirstOrDefault(c => c.GetCustomAttribute<CopyConstructorAttribute>() != null);
+            // fall back to a parameterless constructor
             if (constructor == null)
-                throw new NullReferenceException($"Type {t} does not have a parameterless constructor with the required visibility");
-            return constructor.Invoke(null);
+                constructor = t.GetConstructor(flags, null, Type.EmptyTypes, null);
+            if (constructor == null)
+                throw new NullReferenceException($"Type {t} does not have a parameterless constructor with the required visibility or a constructor with the CopyConstructorAttribute");
+            return constructor.Invoke(new object[constructor.GetParameters().Length]);
         }
 
     }
+
+    /// <summary>
+    /// An attribute that, when added to a constructor, will make that constructor the one used by <see cref="CopyExtensions.Copy{T}"/>, <see cref="CopyExtensions.DeepCopy{T}"/> and <see cref="CopyExtensions.DeepCopyInto{T}"/>.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Constructor)]
+    public class CopyConstructorAttribute : Attribute {
+
+    }
 }
\ No newline at end of file
diff --git a/Sandbox/GameImpl.cs b/Sandbox/GameImpl.cs
index ca23e65..57300dd 100644
--- a/Sandbox/GameImpl.cs
+++ b/Sandbox/GameImpl.cs
@@ -89,11 +89,11 @@ namespace Sandbox {
             panel.SetData("TestKey", new Vector2(10, 2));
             //Console.WriteLine(panel.GetData<Vector2>("TestKey"));
 
-            var obj = new Test {
+            var obj = new Test(Vector2.One, "test") {
                 Vec = new Vector2(10, 20),
                 Point = new Point(20, 30),
                 Dir = Direction2.Left,
-                OtherTest = new Test {
+                OtherTest = new Test(Vector2.One, "other") {
                     Vec = new Vector2(70, 30),
                     Dir = Direction2.Right
                 }
@@ -110,7 +110,7 @@ namespace Sandbox {
             var copy = obj.DeepCopy();
             Console.WriteLine(copy);
 
-            var intoCopy = new Test {OtherTest = new Test()};
+            var intoCopy = new Test(Vector2.One, "test") {OtherTest = new Test(Vector2.One, "other")};
             obj.DeepCopyInto(intoCopy);
             Console.WriteLine(intoCopy);
 
@@ -234,6 +234,11 @@ namespace Sandbox {
             public Direction2 Dir { get; set; }
             public Test OtherTest;
 
+            [CopyConstructor]
+            public Test(Vector2 test, string test2) {
+                Console.WriteLine("Constructed with " + test + ", " + test2);
+            }
+
             public override string ToString() {
                 return $"{this.GetHashCode()}: {nameof(this.Vec)}: {this.Vec}, {nameof(this.Point)}: {this.Point}, {nameof(this.OtherTest)}: {this.OtherTest}, {nameof(this.Dir)}: {this.Dir}";
             }