add CreateBinaryOpForProps

csharp/Lib/Utils/Operators.cs

@@ -0,0 +1,95 @@
+using System.Reflection;
+using static System.Reflection.BindingFlags;
+
+namespace InnovEnergy.Lib.Utils;
+
+public static class Operators
+{
+    public static Func<T, T, T> CreateBinaryOpForProps<T>(this String op) 
+    {
+        var methodName = GetMethodNameForBinaryOp(op);
+
+        var props = typeof(T)
+                   .GetProperties(Instance | Public)
+                   .Where(p => p.CanWrite)
+                   .Select(p => 
+                       (
+                           prop: p,
+                           op: GetOpMethod(methodName, p.PropertyType) ??
+                               throw new ArgumentException($"Type {p.PropertyType.Name} " +
+                                                           $"of property {p.Name} " +
+                                                           $"has no suitable {op} operator defined."))
+                   )
+                   .ToArray();
+
+        var ctr = typeof(T).GetConstructors().FirstOrDefault(c => c.GetParameters().Length == 0);
+        
+        if (ctr is null)
+            throw new ArgumentException($"Type {typeof(T).Name} has no suitable parameterless constructor.");
+
+
+        T Op(T left, T right)
+        {
+            // TODO: make this faster/nicer using Expression API (low prio)
+            
+            var result = ctr.Invoke(null);
+            
+            foreach (var (p, m) in props)
+            {
+                var l = p.GetValue(left);
+                var r = p.GetValue(right);
+
+                var s = m.Invoke(null, new[] { l, r });
+                
+                p.SetValue(result, s);
+            }
+
+            return (T) result;
+        }
+
+        return Op;
+    }
+
+    private static String GetMethodNameForBinaryOp(String op)
+    {
+        // from https://stackoverflow.com/a/29495075
+        
+        return op switch
+        {
+            "&"  => "op_BitwiseAnd",
+            "|"  => "op_BitwiseOr",
+            "+"  => "op_Addition",
+            "-"  => "op_Subtraction",
+            "/"  => "op_Division",
+            "%"  => "op_Modulus",
+            "*"  => "op_Multiply",
+            "<<" => "op_LeftShift",
+            ">>" => "op_RightShift",
+            "^"  => "op_ExclusiveOr",
+            "==" => "op_Equality",
+            "!=" => "op_Inequality",
+            ">"  => "op_GreaterThan",
+            "<"  => "op_LessThan",
+            ">=" => "op_GreaterThanOrEqual",
+            "<=" => "op_LessThanOrEqual",
+            _    => throw new ArgumentException("unknown operator", nameof(op))
+        };
+    }
+
+    private static MethodInfo? GetOpMethod(String? methodName, Type type)
+    {
+        return type
+              .GetMethods(Static | Public)
+              .FirstOrDefault(m => m.Name == methodName
+                                && m.ReturnType == type
+                                && m.IsMonoidOp());
+    }
+
+    private static Boolean IsMonoidOp(this MethodInfo m)
+    {
+        var ps = m.GetParameters();
+
+        return ps.Length == 2 &&
+               ps.All(p => p.ParameterType == m.ReturnType);
+    }    
+}