Added from_table()

limmutable.c

@@ -36,7 +36,11 @@ static int Lcreate_instance(lua_State *L)
     // Stack: [__fields]
     size_t n = lua_objlen(L,-1);
     if ((size_t)n_args-1 != n) {
-        lua_pushstring(L, "incorrect number of arguments");
+        lua_pushstring(L, "incorrect number of arguments: expected ");
+        lua_pushinteger(L, n);
+        lua_pushstring(L, ", but got ");
+        lua_pushinteger(L, n_args-1);
+        lua_concat(L, 4);
         lua_error(L);
     }
     lua_pop(L,1);
@@ -170,6 +174,32 @@ static int Lcreate_instance(lua_State *L)
     return 1;
 }
 
+static int Lfrom_table(lua_State *L)
+{
+    lua_pushvalue(L, 1);
+    // Stack: [mt]
+    lua_getfield(L, -1, "__fields");
+    // Stack: [mt, fields]
+    lua_pushnil(L);
+    int num_args = 0;
+    while (lua_next(L, -2) != 0) {
+        // Stack: [mt, fields, i, field_i]
+        lua_gettable(L, 2);
+        // Stack: [mt, fields, i, table[field_i]]
+        lua_insert(L, -3);
+        // Stack: [mt, table[field_i], fields, i]
+        num_args++;
+    }
+    // Stack: [mt, table[field], ..., fields]
+    lua_pop(L, 1);
+    // Stack: [mt, table[field], ...]
+    lua_pushcfunction(L, Lcreate_instance);
+    // Stack: [mt, table[field], ..., create]
+    lua_insert(L, -(num_args+2));
+    // Stack: [create, mt, table[field_1], ...]
+    lua_call(L, num_args+1, 1);
+    return 1;
+}
 
 static int Llen(lua_State *L)
 {
@@ -351,6 +381,7 @@ static const luaL_Reg R[] =
     { "__index", Lindex},
     { "__ipairs", Lipairs},
     { "__pairs", Lpairs},
+    { "from_table", Lfrom_table},
     { NULL, NULL}
 };
 

test.lua

@@ -73,6 +73,11 @@ end)
 test("Testing tostring", function()
     assert(tostring(v) == "Vec(1, 3)")
 end)
+
+test("Testing from_table", function()
+    assert(Vec:from_table({y=3,x=1}) == v)
+end)
+
 test("Testing singletons", function()
     also_v = Vec(1,3)
     assert(v == also_v)