refactor: pass type to checkUserdata and testUserdata

Rather than pass a string and require an opaque cast, the functions now
accept a Zig type so the string and cast can be done automatically.

Author: natecraddock

src/tests.zig

@@ -1475,7 +1475,7 @@ test "userdata" {
 
     const checkUdata = ziglua.wrap(struct {
         fn inner(l: *Lua) i32 {
-            const ptr = ziglua.opaqueCast(Type, l.checkUserdata(1, "Type"));
+            const ptr = l.checkUserdata(Type, 1);
             if (ptr.a != 1234) {
                 l.pushBytes("error!");
                 l.raiseError();
@@ -1497,10 +1497,10 @@ test "userdata" {
 
     const testUdata = ziglua.wrap(struct {
         fn inner(l: *Lua) i32 {
-            const ptr = ziglua.opaqueCast(Type, l.testUserdata(1, "Type") catch {
+            const ptr = l.testUserdata(Type, 1) catch {
                 l.pushBytes("error!");
                 l.raiseError();
-            });
+            };
             if (ptr.a != 1234) {
                 l.pushBytes("error!");
                 l.raiseError();
@@ -1533,6 +1533,4 @@ test "refs" {
     // probably not needed in ziglua
     _ = Lua.execResult;
     _ = Lua.fileResult;
-
-    _ = Lua.testUserdata;
 }

src/ziglua.zig

@@ -1383,10 +1383,9 @@ pub const Lua = struct {
 
     /// Checks whether the function argument `arg` is a userdata of the type `type_name`
     /// Returns the userdata's memory-block address
-    /// TODO: accept type as param?
-    pub fn checkUserdata(lua: *Lua, arg: i32, type_name: [:0]const u8) *anyopaque {
+    pub fn checkUserdata(lua: *Lua, comptime T: type, arg: i32) *T {
         // the returned pointer will not be null
-        return c.luaL_checkudata(lua.state, arg, type_name).?;
+        return opaqueCast(T, c.luaL_checkudata(lua.state, arg, @typeName(T)).?);
     }
 
     /// Checks whether the code making the call and the Lua library being called are using
@@ -1614,9 +1613,9 @@ pub const Lua = struct {
     }
 
     /// This function works like `Lua.checkUserdata()` except it returns a Zig error instead of raising a Lua error on fail
-    pub fn testUserdata(lua: *Lua, arg: i32, type_name: [:0]const u8) !*anyopaque {
-        if (c.luaL_testudata(lua.state, arg, type_name)) |ptr| {
-            return ptr;
+    pub fn testUserdata(lua: *Lua, comptime T: type, arg: i32) !*T {
+        if (c.luaL_testudata(lua.state, arg, @typeName(T))) |ptr| {
+            return opaqueCast(T, ptr);
         } else return error.Fail;
     }