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@ -188,6 +188,10 @@ some sense "fundamental". All the others can be understood by analogy to the oth
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* `*const T` follows the logic of `&T`
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* `*mut T` follows the logic of `&mut T` (or `UnsafeCell<T>`)
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For more types, see the ["Variance" section][variance-table] on the reference.
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[variance-table]: ../reference/subtyping.html#variance
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> NOTE: the *only* source of contravariance in the language is the arguments to
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> a function, which is why it really doesn't come up much in practice. Invoking
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> contravariance involves higher-order programming with function pointers that
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@ -265,7 +269,7 @@ enough into the place expecting something long-lived.
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Here it is:
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```rust,ignore
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```rust,compile_fail
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fn evil_feeder<T>(input: &mut T, val: T) {
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*input = val;
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}
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@ -285,15 +289,16 @@ And what do we get when we run this?
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```text
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error[E0597]: `spike` does not live long enough
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--> src/main.rs:9:32
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--> src/main.rs:9:31
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9 | let spike_str: &str = &spike;
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| ^^^^^ borrowed value does not live long enough
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10 | evil_feeder(&mut mr_snuggles, spike_str);
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6 | let mut mr_snuggles: &'static str = "meow! :3"; // mr. snuggles forever!!
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| ------------ type annotation requires that `spike` is borrowed for `'static`
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...
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9 | let spike_str: &str = &spike; // Only lives for the block
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| ^^^^^^ borrowed value does not live long enough
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10 | evil_feeder(&mut mr_snuggles, spike_str); // EVIL!
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11 | }
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| - borrowed value only lives until here
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= note: borrowed value must be valid for the static lifetime...
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| - `spike` dropped here while still borrowed
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```
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Good, it doesn't compile! Let's break down what's happening here in detail.
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