Add a conversion from &str to CompleteStr #725
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added 2 commits
March 28, 2018 11:21
This change is necessary because of how Rust tracks lifetimes and reference collapse. The Deref trait returns a reference to the interior of a Complete struct, and does NOT copy out the interior reference. This means that anything consuming the reference coming out of Deref::deref loses awareness of the lifetime of the /referent/, and only knows the lifetime of the Complete struct, which is practically always the local scope. Furthermore, a From impl is added to take an &'anon &'a Inner and build a fresh Complete type with the correct lifetime parameter, NOT the 'anon lifetime generated by Deref::deref. As a result of this change, the following formerly-invalid code is now valid: ```rust let x: Complete; let y: Complete = x.deref().into(); ``` The second Complete will have the same lifetime parameter as the first, and will not have the lifetime parameter of the first's *scope*.
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Despite the title, this PR operates on both |
myrrlyn
commented
Apr 4, 2018
| fn deref(&self) -> &str { | ||
| self.0 | ||
| fn deref(&self) -> &Self::Target { | ||
| &self.0 |
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The value returned from Deref::deref is now an &'_ &'a str, suitable for reconstruction into a CompleteStr<'a> via the From impl above. Formerly, the value returned was an &'_ str where the reference lifetime was tied to the newtype wrapper, not to the referent str, which was impossible to unify during From.
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thanks, this looks good :) |
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This commit expands on the addition of
Deref<Target=&str>and provides a means of downcasting an&strinto aCompleteStr.This should not be used arbitrarily, but is an excellent convenience for manipulating
CompleteStrs using&strmethods. Since theDerefwork always returns bare&strs, even from string slices that are known to beCompleteStr, converting back intoCompleteStris safe and useful.