cleanup TODO's

TypeMagic.pas

@@ -0,0 +1,68 @@
+unit TypeMagic;
+
+interface
+
+type
+
+  {$region Convert}
+
+  ConvertTo<T> = sealed class
+
+    private constructor := raise new System.InvalidOperationException;
+
+    public static function FromChecked<T2>(o: T2): T;
+    public static function FromUnchecked<T2>(o: T2): T;
+    public static function From<T2>(o: T2; checked: boolean := true) :=
+      if checked then FromChecked(o) else FromUnchecked(o);
+
+  end;
+
+  {$endregion Convert}
+
+implementation
+
+uses System.Linq.Expressions;
+
+{$region Convert}
+
+type ConvertCache<T1,T2> = sealed class
+
+  private constructor := raise new System.InvalidOperationException;
+
+  public static checked, unchecked: T2->T1;
+  private static function MakeFunc(conv: (Expression,System.Type)->Expression): T2->T1;
+  begin
+    try
+      var p := Expression.Parameter(typeof(T2));
+      var c := conv(p, typeof(T1));
+      var l := Expression.Lambda&<Func<T2, T1>>(c, p);
+      Result := l.Compile();
+    except
+      on e: Exception do
+      begin
+        Result := o->
+        begin
+          Result := default(T1);
+          raise new System.InvalidCastException($'Failed to make [{TypeToTypeName(typeof(T2))}]=>[{TypeToTypeName(typeof(T1))}] conversion', e);
+        end;
+        exit;
+      end;
+    end;
+
+  end;
+  static constructor;
+  begin
+    checked := MakeFunc(Expression.ConvertChecked);
+    unchecked := MakeFunc(Expression.Convert);
+  end;
+
+end;
+
+static function ConvertTo<T>.FromChecked<T2>(o: T2) :=
+  ConvertCache&<T,T2>.checked(o);
+static function ConvertTo<T>.FromUnchecked<T2>(o: T2) :=
+  ConvertCache&<T,T2>.unchecked(o);
+
+{$endregion Convert}
+
+end.