'Store the LLVM *value* into the field at *index*.'

def __setitem__(self, index, value):

    ptr = self._get_ptr_by_index(index)
    if (ptr.type.pointee != value.type):
        fmt = 'Type    mismatch:    __setitem__(%d,    ...)    expected    %r    but    got    %r'
        raise AssertionError((fmt % (index, str(ptr.type.pointee), str(value.type))))
    self._builder.store(value, ptr)
