72 lines
2.6 KiB
Rust
72 lines
2.6 KiB
Rust
use std::path::Path;
|
|
|
|
fn main() {
|
|
|
|
}
|
|
|
|
#[derive(Copy, Clone, Debug)]
|
|
struct CopyObject<'a> {
|
|
pub val: &'a str,
|
|
}
|
|
|
|
struct AnObject {
|
|
pub val: String,
|
|
}
|
|
|
|
struct TheOtherObject {
|
|
pub val: Vec<u8>,
|
|
}
|
|
|
|
impl AnObject {
|
|
|
|
// as_ borrowed (&self) -> borrowed (&[u8])
|
|
fn as_bytes(&self) -> &[u8] {
|
|
// because the underlying data structure of a String is a Vec<u8>, the as_bytes actually just returns this as a borrowed value, really just making this a dumb proxy, but it shows us what we want: as_ is just a view into the underlying data structure: nothing is copied, nothing new is created, it only exposes the underlying data: free as in free beer because we are just returning something that point to something else: a reference
|
|
self.val.as_bytes()
|
|
}
|
|
|
|
// to_ borrowed (&self) -> borrowed (&[u8])
|
|
fn to_guarded_bytes(&self) -> Option<&[u8]> {
|
|
// this is really a dumb example, but it kind of proves the point: we convert our Target to a str. The input and output smells like the above as_ and the as_ is free, but this really isn't, because we are doing some expensive validation first
|
|
let mut is_valid = true;
|
|
|
|
for s in self.val.chars() {
|
|
if s > 'b' && s < 'w' {
|
|
is_valid = false;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if is_valid {
|
|
return Some(self.val.as_bytes());
|
|
}
|
|
|
|
None
|
|
}
|
|
|
|
// to_ borrowed (&self) -> owned (TheOtherObject) (non-copy types)
|
|
fn to_guarded_object(&self) -> Option<TheOtherObject> {
|
|
// This performs our previous check, and if everything is fine, it converts our object to the new object, simply creating it, and making some more to_ calls. Really expensive, but no copy is made of `self`
|
|
let guarded_bytes = self.to_guarded_bytes();
|
|
|
|
match guarded_bytes {
|
|
Some(bytes) => {
|
|
Some(TheOtherObject {val: bytes.to_vec()})
|
|
},
|
|
None => None
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'a> CopyObject<'a> {
|
|
|
|
// to_ owned (self) -> owned (TheOtherObject) (copy types)
|
|
fn to_object(self) -> TheOtherObject {
|
|
// because self is not a reference, it is actually not consumed (likewise it isn't consumed when we do a &self ... yes we could do a &self here, but it kind of defeats the purpose of doing the example), but it is copied. The copy itself though is more expensive than just doing a reference. In our example, we are actually being quite expensive doing a to_vec conversion of our free as_ view
|
|
|
|
TheOtherObject { val: self.val.as_bytes().to_vec()}
|
|
}
|
|
}
|
|
|
|
// into_ owned -> owned (non-copy types)
|