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Clarify order-of-execution

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varkor 2020-04-14 21:10:48 +01:00
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text/0000-destructuring-assignment.md
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@ -149,14 +149,16 @@ e.g. how this could interact with custom implementations of the operators.
## Order-of-assignment ## Order-of-assignment
The right-hand side of the assignment is always performed first. Then, assignments are performed left-to-right. Note that component expressions in the left-hand side may be complex, not simply identifiers, and may require execution to resolve to lvalues.
In a declaration, each identifier may be bound at most once. That is, the following is invalid: In a declaration, each identifier may be bound at most once. That is, the following is invalid:
```rust ```rust
let (a, a) = (1, 2); let (a, a) = (1, 2);
``` ```
For destructuring assignments, we currently permit assignments containing identical identifiers, with assignments performed left-to-right. However, these trigger an "unused assignment" For destructuring assignments, we currently permit assignments containing identical identifiers. However, these trigger an "unused assignment"
warning. Assignments are performed left-to-right. warning.
```rust ```rust
(a, a) = (1, 2); // warning: value assigned to `a` is never read (a, a) = (1, 2); // warning: value assigned to `a` is never read