Depends on the language, but I prefer the Python approach here. Python is a dynamically (but strongly) typed language. If you want a list from a dict, get a new list via casting ie. list(the_dict), or get a list from either side via the_dict.keys() or the_dict.values(). Weakly typed languages that will do implicit type conversion for you such as TCL and Perl seems prone to mistakes and confusion from this stuff as code complexity of the project grows. I don't think Python gets it right here either though really, as in the end explicit types save so much headache and stupid bugs by finding problems for you at lint or compile time.