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Update lifetimes-function-calls.md ()

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* Update lifetimes-function-calls.md

I am trying to describe the problem lifetimes solve. It may seem they are complex and useless, but the paragraph starts from the problem Rust cannot
solve on it's own (yet). Then the paragraph illustrates the problem represented in the code and how lifetimes solve it.

* Update lifetimes-function-calls.md

Moving the generic explanation of why lifetimes are important to the speaker notes.

* Make language more direct

Co-authored-by: Martin Geisler <martin@geisler.net>
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Igor Petruk 2023-01-24 08:50:05 +00:00 committed by GitHub
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src/ownership/lifetimes-function-calls.md

@ -50,5 +50,11 @@ In the above example, try the following:
Note how this does not compile since `p3` outlives `p2`.
* Reset the workspace and change the function signature to `fn left_most<'a, 'b>(p1: &'a Point, p2: &'a Point) -> &'b Point`. This will not compile because the relationship between the lifetimes `'a` and `'b` is unclear.
* Another way to explain it:
* Two references to two values are borrowed by a function and the function returns
another reference.
* It must have come from one of those two inputs (or from a global variable).
* Which one is it? The compiler needs to to know, so at the call site the returned reference is not used
for longer than a variable from where the reference came from.
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