def augment(self, other):
        """
        Augment this function type with the other function types' templates,
        so as to support more input types.
        """
        if type(other) is type(self) and other.typing_key == self.typing_key:
            return type(self)(self.templates + other.templates)

        Augment this function type with the other function types' templates,
        so as to support more input types.
        
numba/core/types/functions.py