explanatory commentlibrary-module

1 files changed, 4 insertions, 1 deletions

diff --git a/cffi/vengine_gen.py b/cffi/vengine_gen.py
index a2a6e78..27fe82c 100644
--- a/cffi/vengine_gen.py
+++ b/cffi/vengine_gen.py
@@ -57,7 +57,10 @@ class VGenericEngine(object):
         # the C compiler
         self._load(module, 'loading')
 
-        # build the FFILibrary class and instance
+        # build the FFILibrary class and instance, this is a module subclass
+        # because modules are expected to have usually-constant-attributes and
+        # in PyPy this means the JIT is able to treat attributes as constant,
+        # which we want.
         class FFILibrary(types.ModuleType):
             _cffi_generic_module = module
             _cffi_ffi = self.ffi