class level inheritance, changed class representation slightly

Looking up a class property will now search the parent class properties
if parent exists

Classes have a few more built in properties:

  * __name holds the name of the class as it was defined as a string
  * __base holds the instance metatable as it was defined (not dynamic)
  * __parent holds the class's parent class if it exists (not dynamic)

The way class inheritance is handled was CHANGED (uses __base instead of
looking at __index of parents metatable). Make sure you recompile all
your code if using class inheritance because old classes won't work with
new ones.

Author: leafo

moonscript/transform.lua

@@ -638,12 +638,69 @@ Statement = Transformer({
       {
         "__init",
         constructor
+      },
+      {
+        "__base",
+        base_name
+      },
+      {
+        "__name",
+        {
+          "string",
+          '"',
+          name
+        }
+      },
+      {
+        "__parent",
+        parent_cls_name
+      }
+    })
+    local class_lookup = build["if"]({
+      cond = {
+        "exp",
+        "val",
+        "==",
+        "nil",
+        "and",
+        parent_cls_name
+      },
+      ["then"] = {
+        parent_cls_name:index("name")
+      }
+    })
+    insert(class_lookup, {
+      "else",
+      {
+        "val"
       }
     })
     local cls_mt = build.table({
       {
         "__index",
-        base_name
+        build.fndef({
+          args = {
+            {
+              "cls"
+            },
+            {
+              "name"
+            }
+          },
+          body = {
+            build.assign_one(LocalName("val"), build.chain({
+              base = "rawget",
+              {
+                "call",
+                {
+                  base_name,
+                  "name"
+                }
+              }
+            })),
+            class_lookup
+          }
+        })
       },
       {
         "__call",
@@ -779,16 +836,10 @@ Statement = Transformer({
                 {
                   base_name,
                   _with_0.chain({
-                    base = "getmetatable",
-                    {
-                      "call",
-                      {
-                        parent_cls_name
-                      }
-                    },
+                    base = parent_cls_name,
                     {
                       "dot",
-                      "__index"
+                      "__base"
                     }
                   })
                 }

moonscript/transform.moon

@@ -353,10 +353,30 @@ Statement = Transformer {
 
     cls = build.table {
       {"__init", constructor}
+      {"__base", base_name}
+      {"__name", {"string", '"', name}} -- "quote the string"
+      {"__parent", parent_cls_name}
     }
 
+    -- look up a name in the class object
+    class_lookup = build["if"] {
+      cond: {"exp", "val", "==", "nil", "and", parent_cls_name}
+      then: {
+        parent_cls_name\index"name"
+      }
+    }
+    insert class_lookup, {"else", {"val"}}
+
     cls_mt = build.table {
-      {"__index", base_name}
+      {"__index", build.fndef {
+        args: {{"cls"}, {"name"}}
+        body: {
+          build.assign_one LocalName"val", build.chain {
+            base: "rawget", {"call", {base_name, "name"}}
+          }
+          class_lookup
+        }
+      }}
       {"__call", build.fndef {
         args: {{"cls"}, {"..."}}
         body: {
@@ -421,11 +441,10 @@ Statement = Transformer {
           then: {
             .chain {
               base: "setmetatable"
-              {"call", {base_name, .chain {
-                base: "getmetatable"
-                {"call", {parent_cls_name}}
-                {"dot", "__index"}
-              }}}
+              {"call", {
+                base_name,
+                .chain { base: parent_cls_name,  {"dot", "__base"}}
+              }}
             }
           }
         }