E0512 rust type_error ai_generated true

error[E0512]: cannot transmute between types of different sizes, or dependently-sized types

ID: rust/e0512-cannot-transmute-different-sizes

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85%Fix Rate
87%Confidence
1Evidence
2023-03-22First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.64.0 active — — —
1.67.0 active — — —
1.71.0 active — — —

Root Cause

Using `std::mem::transmute` to convert between types with mismatched sizes (e.g., `u32` to `u64`).

generic

中文

使用 `std::mem::transmute` 在大小不匹配的类型之间进行转换（例如 `u32` 到 `u64`）。

Official Documentation

https://doc.rust-lang.org/error_codes/E0512.html

Workarounds

  1. 95% success Use safe conversions: `u64::from(u32_val)` or `u32_val as u64` for numeric widening. 
    Use safe conversions: `u64::from(u32_val)` or `u32_val as u64` for numeric widening.
  2. 80% success For structs, use `bytemuck::cast` or `unsafe { transmute_copy }` with explicit size checks. 
    For structs, use `bytemuck::cast` or `unsafe { transmute_copy }` with explicit size checks.

中文步骤

  1. 使用安全转换：`u64::from(u32_val)` 或 `u32_val as u64` 进行数值拓宽。
  2. 对于结构体，使用 `bytemuck::cast` 或 `unsafe { transmute_copy }` 并显式检查大小。

Dead Ends

Common approaches that don't work:

  1. Using `unsafe { transmute::<u32, u64>(val) }` without checking size 100% fail

    Compiler catches size mismatch; transmute requires same layout and size.

  2. Adding `#[repr(C)]` to custom types without ensuring alignment 90% fail

    Doesn't change the size; only affects layout, not total byte count.