Restrictions on moves into and out-from fixed-length arrays. #21930
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Now this is no longer legal: `fn foo(arr: [D; 5]) -> D { arr[2] }`,
unless `D` implements `Copy`.
This "move out-from" restriction only applies to `expr[i]`, and not
destructuring bind (e.g. `f([a, b, c]: Array) { ... }`).
See discussion on RFC PR 533.
[breaking-change]
…[i]`.
No longer legal: `fn foo(a: [D; 5]) { drop(a); a[2] = D::new(); }`;
one must first initialize the entirety of `a` before assigning
to individual elements.
See discussion on RFC PR 533.
[breaking-change]
Note that the change to the error message in borrowck-use-in-index-lvalue.rs, where we report that `*w` is uninitialized rather than `w`, was unintended fallout from the implementation strategy used here. The change appears harmless to me, but I welcome advice on how to bring back the old message, which was slightly cleaner (i.e. less unintelligible).
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(rust_highfive has picked a reviewer for you, use r? to override) |
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(closing for now; I will attempt to try a mem_categorization based approach as @nikomatsakis suggests.) |
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…komatsakis Revised version of PR #21930. Restrictions on moves into and out-from fixed-length arrays. (There was only one use of this "feature" in the compiler source.) Note 1: the change to the error message in tests/compile-fail/borrowck-use-in-index-lvalue.rs, where we now report that *w is uninitialized (rather than w), was unintended fallout from the implementation strategy used here. The change appears harmless to me, but I welcome advice on how to bring back the old message, which was slightly cleaner (i.e. less unintelligible) since that the syntactic form *w does not actually appear in the source text. Note 2: the move out-from restriction to only apply to expr[i], and not destructuring bind (e.g. f([a, b, c]: Array) { ... }) since the latter is compatible with nonzeroing drop, AFAICT. [breaking-change]
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Restrictions on moves into and out-from fixed-length arrays.
(There was only one use of this "feature" in the compiler source.)
Note 1: the change to the error message in
tests/compile-fail/borrowck-use-in-index-lvalue.rs, where we now report that*wis uninitialized (rather thanw), was unintended fallout from the implementation strategy used here. The change appears harmless to me, but I welcome advice on how to bring back the old message, which was slightly cleaner (i.e. less unintelligible) since that the syntactic form*wdoes not actually appear in the source text.Note 2: the move out-from restriction to only apply to
expr[i], and not destructuring bind (e.g.f([a, b, c]: Array) { ... }) since the latter is compatible with nonzeroing drop, AFAICT.borrowck::gather_loans::gather_moves, and welcome suggestions on ways to do it without accessing theast_map, but preferably also without changing theexpr_use_visitorAPI.)This addresses RFC PR 533: rust-lang/rfcs#533 (which is not yet merged).
[breaking-change]