{
  "$type": "site.standard.document",
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  "path": "/t/interiorassign-trait-a-b/24291#post_18",
  "publishedAt": "2026-05-10T20:35:40.000Z",
  "site": "https://internals.rust-lang.org",
  "textContent": "Another use case for an overloadable assignment unrelated to interior mutability is inserting items into a `HashMap`, which currently cannot be done using `map[key] = ...` syntax, because it could not avoid panicking on an absent key, because right now the only trait for this is `IndexMut` which requires returning `&mut` to an _existing, initialized_ place. In general, Rust assignment currently demands `&mut`, but producing `&mut` is not always possible or wise even when an assignment-like operation is possible.",
  "title": "InteriorAssign trait { a := b }"
}