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72 lines
2.6 KiB
72 lines
2.6 KiB
use std::path::Path;
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fn main() {
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}
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#[derive(Copy, Clone, Debug)]
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struct CopyObject<'a> {
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pub val: &'a str,
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}
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struct AnObject {
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pub val: String,
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}
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struct TheOtherObject {
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pub val: Vec<u8>,
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}
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impl AnObject {
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// as_ borrowed (&self) -> borrowed (&[u8])
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fn as_bytes(&self) -> &[u8] {
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// 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
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self.val.as_bytes()
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}
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// to_ borrowed (&self) -> borrowed (&[u8])
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fn to_guarded_bytes(&self) -> Option<&[u8]> {
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// 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
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let mut is_valid = true;
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for s in self.val.chars() {
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if s > 'b' && s < 'w' {
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is_valid = false;
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break;
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}
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}
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if is_valid {
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return Some(self.val.as_bytes());
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}
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None
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}
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// to_ borrowed (&self) -> owned (TheOtherObject) (non-copy types)
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fn to_guarded_object(&self) -> Option<TheOtherObject> {
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// 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`
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let guarded_bytes = self.to_guarded_bytes();
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match guarded_bytes {
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Some(bytes) => {
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Some(TheOtherObject {val: bytes.to_vec()})
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},
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None => None
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}
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}
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}
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impl<'a> CopyObject<'a> {
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// to_ owned (self) -> owned (TheOtherObject) (copy types)
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fn to_object(self) -> TheOtherObject {
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// 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
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TheOtherObject { val: self.val.as_bytes().to_vec()}
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}
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}
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// into_ owned -> owned (non-copy types)
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