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by codedokode 414 days ago
The functions are so verbose and inconvenient that even Rust developers themselves do not use them. For example, in this code [1] they used a wrapping addition instead of "checked_add" because it is faster to write.

For comparison, Swift uses "+" for checked addition and as a result, majority of developers use checked addition by default. And in Rust due to its poor design choices most developers use wrapping addition even where a checked addition should be used.

[1] https://doc.rust-lang.org/src/alloc/vec/mod.rs.html#2010
2 comments
genrilz 414 days ago
The reason '+ 1' is fine in the example you gave is that length is always less than or equal to capacity. If you follow 'grow_one' which was earlier in the function to grow the capacity by one if needed, you will find that it leads to the checked addition in [0], which returns an error that [1] catches and turns into a panic. So using '+1' prevents a redundant check in release mode while still adding the check in debug mode in case future code changes break the 'len <= capacity' invariant.

Of course, if you don't trust the standard library, you can turn on overflow checks in release mode too. However, the standard library is well tested and I think most people would appreciate the speed from eliding redundant checks.

  [0]: https://doc.rust-lang.org/src/alloc/raw_vec.rs.html#651
  [1]: https://doc.rust-lang.org/src/alloc/raw_vec.rs.html#567
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ultimaweapon 414 days ago
Checked addition by default will have too much overhead and it will hurt performance, which unacceptable in Rust since it was designed as a system language. Swift can use checked add by default since it was designed for application software.

Your example code is not because it is faster to write, it is because it is impossible for its to overflow on that line.

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codedokode 414 days ago
Why should checked addition have any overhead? You should just use checked addition instruction (on architectures that support it) instead of wrapping addition.

Or just because on Intel CPUs it has overhead, we must forget about writing safer code?

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