# error[E0308]: mismatched types: expected `usize`, found `u32`

- **ID:** `rust/e0308-expected-usize-found-u32`
- **Domain:** rust
- **Category:** type_error
- **Error Code:** `E0308`
- **Verification:** ai_generated
- **Fix Rate:** 90%

## Root Cause

Using a fixed-size integer (like u32) where a usize is required, typically in array indexing or slice operations.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 1.65 | active | — | — |
| 1.70 | active | — | — |
| 1.75 | active | — | — |

## Workarounds

1. **Convert explicitly with `try_into()`: `let idx: usize = index.try_into().unwrap();`** (95% success)
   ```
   Convert explicitly with `try_into()`: `let idx: usize = index.try_into().unwrap();`
   ```
2. **Use `as` conversion if the value is guaranteed to fit: `let idx = index as usize;`** (85% success)
   ```
   Use `as` conversion if the value is guaranteed to fit: `let idx = index as usize;`
   ```
3. **Change the function signature to accept usize: `fn process(index: usize)`** (90% success)
   ```
   Change the function signature to accept usize: `fn process(index: usize)`
   ```

## Dead Ends

- **Casting with `as`: `index as usize` without checking for overflow on 32-bit platforms** — This works syntactically but may cause silent truncation on 32-bit systems if the u32 value exceeds 2^32. (60% fail)
- **Changing the variable type to usize everywhere** — May break other code that expects u32, and does not address the root cause of type mismatch. (70% fail)