Rust error[E0502]: cannot borrow as mutable because it is also borrowed as immutable

VERIFIED WAYPOINT ⚡ Saves ~48,000 tokens ($0.17) Category: Systems & Memory

🎯 Target Goal & Friction

Goal: Resolve double borrow in Rust iteration using cloned values or block scopes

Error Signature: error[E0502]: cannot borrow `data` as mutable because it is also borrowed as immutable

⚡ Direct Teleport Deep Link (0ms Navigation)

https://doc.rust-lang.org/error_codes/E0502.html →

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Verified Code / Configuration Diff

@@ src/main.rs @@
- for item in &data {
-     data.push(item * 2); // E0502 borrow conflict
- }
+ let items: Vec<_> = data.iter().cloned().collect();
+ for item in items {
+     data.push(item * 2);
+ }

1-Line Instant CLI Fix

cargo clippy

Root Cause & Explanation

Rust memory safety forbids mutating a collection while actively iterating over its immutable reference. Collect cloned keys into an intermediate vector or limit borrow scope.