37 lines
924 B
Markdown
37 lines
924 B
Markdown
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# Indexing
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`TicketStore::get` returns an `Option<&Ticket>` for a given `TicketId`.
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We've seen before how to access elements of arrays and vectors using Rust's
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indexing syntax:
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```rust
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let v = vec![0, 1, 2];
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assert_eq!(v[0], 0);
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```
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How can we provide the same experience for `TicketStore`?
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You guessed right: we need to implement a trait, `Index`!
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## `Index`
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The `Index` trait is defined in Rust's standard library:
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```rust
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// Slightly simplified
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pub trait Index<Idx>
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{
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type Output;
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// Required method
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fn index(&self, index: Idx) -> &Self::Output;
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}
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```
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It has:
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- One generic parameter, `Idx`, to represent the index type
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- One associated type, `Output`, to represent the type we retrieved using the index
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Notice how the `index` method doesn't return an `Option`. The assumption is that
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`index` will panic if you try to access an element that's not there, as it happens
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for array and vec indexing.
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