Nobody Taught You the Function Philosophy. Let Me Fix That.

I've been writing code for a long time, and the one thing that still separates great developers from average ones isn't the language they use. It's how they think about functions. Most tutorials give you steps. Nobody talks about the why. Here is the short version of what I know. A function is a mini machine with one job . You feed it input, it runs its hidden process, and hands you back a result. That's it. If your function is doing three jobs, you don't have a function. You have chaos with a name. The argument rule nobody follows: Zero arguments is the ideal . One is clear. Two is acceptable. Three or more? Just trash your function and rethink the design. When arguments pile up, they are telling you something: they want to become a struct or an object. // Stop doing this fn create_user ( name : & str , email : & str , age : u32 , country : & str ) -> User { ... } // Start doing this fn create_user ( params : NewUserParams ) -> User { ... } Single responsibility is not single line. I