It's about trusting a function call. Imagine the following C functions: extern result fubar(struct foo *); extern result snafu(struct foo const *); J

It's about trusting a function call. Imagine the following C functions: extern result fubar(struct foo *); extern result snafu(struct foo const *); Just by looking at the function prototype, I know that calling snafu() won't change the struct foo I pass it. I don't know what fubar() will do to it. Maybe it won't change, maybe it will. I'd have to check the implementation of fubar() to find out.