Generalize StringMap.opEquals to other values (#378)

* Generalize StringMap.opEquals to other values

* Make StringMap.opEquals @safe along with test

* Use scalar comparison instead of array comparison in static assert

Author: nordlow

source/mir/string_map.d

@@ -41,13 +41,16 @@ struct StringMap(T, U = uint)
 
     ///
     // current implementation is workaround for linking bugs when used in self referencing algebraic types
-    bool opEquals(const StringMap rhs) const
+    bool opEquals(V)(scope const StringMap!(V, U) rhs) const
     {
+        // NOTE: moving this to template restriction fails with recursive template instanation
+        static assert(is(typeof(T.init == V.init) : bool),
+                      "Unsupported rhs of type " ~ typeof(rhs).stringof); // TODO:
         if (keys != rhs.keys)
             return false;
         if (implementation)
             foreach (const i; 0 .. implementation._length)
-                if (implementation._values[i] != rhs.implementation._values[i])
+                if (implementation.values[i] != rhs.implementation.values[i]) // needs `values` instead of `_values` to be @safe
                     return false;
         return true;
     }
@@ -738,6 +741,23 @@ unittest
     assert(table == table);
 }
 
+version(mir_test)
+///
+@safe unittest
+{
+    StringMap!int x;
+    x["L"] = 3;
+    x["A"] = 2;
+    x["val"] = 1;
+
+    StringMap!uint y;
+    y["L"] = 3;
+    y["A"] = 2;
+    y["val"] = 1;
+
+    assert(x == y);
+}
+
 private struct StructImpl(T, U = uint)
     if (!__traits(hasMember, T, "opPostMove") && __traits(isUnsigned, U))
 {