Memory Safety Check Skill

Validate Mojo ownership and borrowing rules.

When to Use

Reviewing code for memory safety
Debugging memory or segfault issues
Before merging code
Performance testing reveals corruption

Quick Reference

# Owned parameter - takes ownership
fn consume(var data: Tensor):
    process(data)  # data moved here

# Borrowed parameter - read-only reference
fn read_only(data: Tensor):
    let value = data[0]  # OK: read-only

# Mutable reference - in-place modification
fn modify(mut data: Tensor):
    data[0] = 42  # Mutate in caller's variable

Workflow

Trace ownership - Which function owns each value
Check borrows - Are references short-lived
Verify moves - Use ^ operator for ownership transfer
Test lifetimes - Compile and run with memory checks
Debug issues - Identify use-after-move or dangling refs

Mojo-Specific Notes

Use ^ operator ONLY when transferring ownership
mut self for mutating methods (NOT out self)
out self ONLY for constructors (__init__)
List/Dict/String are non-copyable - must use ^ when returning

Error Handling

| Error | Cause | Solution | |-------|-------|----------| | Use after move | Variable used after ownership transfer | Create copy or don't move | | Dangling reference | Reference to local variable | Return owned value with ^ | | Mutable aliasing | Multiple mutable refs to same data | Ensure single mutable reference | | Type not copyable | Missing ^ on non-copyable return | Add transfer operator ^ |

References

.claude/shared/mojo-anti-patterns.md - Ownership violations section
.claude/shared/mojo-guidelines.md - Parameter conventions table