I originally wrote a reply here that I deleted because I realised somebody introduced the wrong idea below. Yes, the repeat() function on strings does what you describe.
str::repeat() behaves exactly as you describe. "No".repeat(4) is "NoNoNoNo" and "What".repeat(0) is "" and so on.
Note that str::repeat() returns a String, not a str, because if n > 1 it obviously needs to allocate somewhere to put the String. As a result it is not available in environments which don't have String, like a tiny embedded device - for them str::repeat() does not exist whereas stuff like str::starts_with() and str::split_once() are fine.
Repeat is an iterator, so you can apply it to any type you want, not just strings. You can chain it with other iterators, or collect it into some data structure. But yes, repeat(0) returns an empty iterator.
This example makes a repeat(0) but asks for just the first 12 things in it, they are, of course, all twelve zeroes. Feel free to adjust it to ask for more if you think maybe there aren't any more, or they stop being zero.
