Calling C nested function pointer from Lua
<p>I have the following C struct, that contains function pointer:</p>

<pre><code>struct db {
    struct db_impl *impl;
    void (*test)(struct db *self); // How to invoke it from Lua??
};
void (*db_test)(void); // this I can invoke from Lua

struct db * get_db() {
    // create and init db
    struct db * db = init ...
    db-&gt;test = &amp;db_real_impl; // db_real_impl is some C function
    return db;
}
</code></pre>

<p>So the test function pointer after initialization points to some function.
Now I need to call that function from Lua using FFI library, but it fails with error: <code>'void' is not callable</code>.</p>

<pre><code>local db = ffi.C.get_db()
db.test(db)  -- fails to invoke
-- Error message: 'void' is not callable

ffi.C.db_test()  -- this works fine
</code></pre>

<p>In C the code would be:</p>

<pre><code>struct db *db = get_db();
db-&gt;test(db);
</code></pre>

<p>In Lua I'm able to invoke free function pointers easily, but can't invoke function pointer from struct. How to invoke it from Lua?</p>