lesson 05: change text #99
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wprzytula
requested changes
Oct 22, 2025
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| This eliminates the heap allocations, but there's another catch. What if `NewsArticle` already had another (non-summarizing) `Display` implementation? We would end up in a double-trait-implementation conflict, which is a compile-time error. | ||
| we can see that we do one unnecessary heap allocation that we can optimize. Instead of creating a `String` (which does the heap allocation) that we then pass to `format!`, we can just use `format!` directly: |
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Please leave the previous wording here as well, as it conveys the message about avoiding resource waste more clearly:
The
Summarytrait was really wasteful: it always allocated theStrings on heap, even though we only needed to display the formatted string, and we could do that without allocations.
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| ## Associated types vs `impl Trait` | ||
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| The use of generic types in `Summary` trait makes it semantics like this: | ||
| Rust offers two complementary tools for expressing "some type that implements a trait": | ||
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| > A type can be summarized with any type supporting it. | ||
| - **Associated types** belong to a trait definition. Each implementer fills in the concrete type once, driving a consistent contract across all of the trait's methods. Use them when the trait itself needs to name a type (for example, an iterator's `Item` or a parser's `Output`). They shine when multiple methods must agree on the exact type, or when a caller should be able to refer to it explicitly (`MyIterator::Item`). |
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Before, this section would compare generic traits vs traits with associated types. Now you compare traits with explicitly specified associated types vs impl Trait with implicit associated types. This is entirely a different comparison, and I believe the comparison with generic traits should also be here.
Co-authored-by: Wojciech Przytuła <wp418383@students.mimuw.edu.pl>
Co-authored-by: Wojciech Przytuła <wp418383@students.mimuw.edu.pl>
wprzytula
approved these changes
Oct 22, 2025
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