def f=(k,v)=1
    ^~ invalid method name; a setter method cannot be defined in an endless method definition

def obj.f=(k,v)=1
        ^~ invalid method name; a setter method cannot be defined in an endless method definition

def []=(k,v)=1
    ^~~ invalid method name; a setter method cannot be defined in an endless method definition

def obj.[]=(k,v)=1
        ^~~ invalid method name; a setter method cannot be defined in an endless method definition