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Add safety comment.

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Andrew Walbran
2023-01-17 16:35:39 +00:00
parent 47e28e87c0
commit d07171e76d
1 changed files with 4 additions and 2 deletions
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6
src/unsafe/unsafe-functions.md
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@ -1,13 +1,15 @@
# Calling Unsafe Functions # Calling Unsafe Functions
A function or method can be marked `unsafe` if it has extra preconditions you A function or method can be marked `unsafe` if it has extra preconditions you
must uphold: must uphold to avoid undefined behaviour:
```rust,editable ```rust,editable
fn main() { fn main() {
let emojis = "🗻∈🌏"; let emojis = "🗻∈🌏";
// Safe because the indices are in the correct order, within the bounds of
// the string slice, and lie on UTF-8 sequence boundaries.
unsafe { unsafe {
// Undefined behavior if indices do not lie on UTF-8 sequence boundaries.
println!("{}", emojis.get_unchecked(0..4)); println!("{}", emojis.get_unchecked(0..4));
println!("{}", emojis.get_unchecked(4..7)); println!("{}", emojis.get_unchecked(4..7));
println!("{}", emojis.get_unchecked(7..11)); println!("{}", emojis.get_unchecked(7..11));