Make primitive refs (i.e. pointers to numbers, etc) behave as arrays.

LUA_API.rst

@@ -121,6 +121,12 @@ or as a result of calling the ``_field()`` method.
 
 They behave as structs with one field ``value`` of the right type.
 
+To make working with numeric buffers easier, they also allow
+numeric indices. Note that other than excluding negative values
+no bound checking is performed, since buffer length is not available.
+Index 0 is equivalent to the ``value`` field.
+
+
 Struct references
 -----------------
 

Lua API.html

@@ -453,6 +453,10 @@ that don't fit any of the other reference types. Such
 references can only appear as a value of a pointer field,
 or as a result of calling the <tt class="docutils literal">_field()</tt> method.</p>
 <p>They behave as structs with one field <tt class="docutils literal">value</tt> of the right type.</p>
+<p>To make working with numeric buffers easier, they also allow
+numeric indices. Note that other than excluding negative values
+no bound checking is performed, since buffer length is not available.
+Index 0 is equivalent to the <tt class="docutils literal">value</tt> field.</p>
 </div>
 <div class="section" id="struct-references">
 <h3><a class="toc-backref" href="#id4">Struct references</a></h3>

library/LuaTypes.cpp

@@ -635,6 +635,28 @@ static int meta_struct_next(lua_State *state)
     return 2;
 }
 
+/**
+ * Field lookup for primitive refs: behave as a quasi-array with numeric indices.
+ */
+static type_identity *find_primitive_field(lua_State *state, int field, const char *mode, uint8_t **ptr)
+{
+    if (lua_type(state, field) == LUA_TNUMBER)
+    {
+        int idx = lua_tointeger(state, field);
+        if (idx < 0)
+            field_error(state, 2, "negative index", mode);
+
+        lua_rawgetp(state, UPVAL_METATABLE, &DFHACK_IDENTITY_FIELD_TOKEN);
+        auto id = (type_identity *)lua_touserdata(state, -1);
+        lua_pop(state, 1);
+
+        *ptr += int(id->byte_size()) * idx;
+        return id;
+    }
+
+    return (type_identity*)find_field(state, field, mode);
+}
+
 /**
  * Metamethod: __index for primitives, i.e. simple object references.
  *   Fields point to identity, or NULL for metafields.
@@ -642,7 +664,7 @@ static int meta_struct_next(lua_State *state)
 static int meta_primitive_index(lua_State *state)
 {
     uint8_t *ptr = get_object_addr(state, 1, 2, "read");
-    auto type = (type_identity*)find_field(state, 2, "read");
+    auto type = find_primitive_field(state, 2, "read", &ptr);
     if (!type)
         return 1;
     type->lua_read(state, 2, ptr);
@@ -655,7 +677,7 @@ static int meta_primitive_index(lua_State *state)
 static int meta_primitive_newindex(lua_State *state)
 {
     uint8_t *ptr = get_object_addr(state, 1, 2, "write");
-    auto type = (type_identity*)find_field(state, 2, "write");
+    auto type = find_primitive_field(state, 2, "write", &ptr);
     if (!type)
         field_error(state, 2, "builtin property or method", "write");
     type->lua_write(state, 2, ptr, 3);