Function kul::source_stream::to_rc_box_str

pub fn to_rc_box_str(s: String) -> Rc<Box<str>>

Converting a String to a boxed str slice gives the program a chance to use minimal memory by freeing the String's extra capacity.

This might cheaply convert in place, because it only shrinks the allocated size if the String's capacity is greater than its length (but this is likely), and the allocator has a chance to not move it if reallocation is done and a chance to free and reuse the extra capacity (depending on the allocator used). But the allocator might move it, which is a cost, but this might be acceptable for the application because that one-time performance cost could be worth giving it the chance to reclaim unused memory from these now-immutable strings which might live a long time.

But the additional disadvantage of Rc<Box<str>> is that there is an extra level of pointer indirection compared to Rc<str>, which could impact cache locality. However, converting to Rc<str> always must move the string contents and never has the chance of cheaply converting in place.