A new assignment operator for functions

Ideas
1

My idea is fairly simple: assignment operator for a class’ functions.
Example:

string = string.replace(‘a’, ‘b’)

string .= relplace(‘a’, ‘b’)

2

I’m not a fan because you can’t have arbitrary expressions on the right hand side, which diverges too much from how the other compound assignment operators work. For example, this makes no sense, and should presumably be a SyntaxError:

foo .= 3