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> > The metatable of `string` is itself.  It has a method __index.
> > So it seems to be a feature, not a bug. :-)
> Yes. But I cannot see what can be that feature.
> >From the sources, the __index field inside `string` is a function
> whose only purpose is to throw an error.
> Why is that function needed?? In all other module tables (like table,
> os, io, ...) indexing the table with an non-existent field simply
> returns nil.

It is used to detect errors like this:


You should use 'rawget' in your tests for an __index field. (That is
how Lua accesses those fields, after all.)

-- Roberto