Destruction and __del__

When a value is no longer needed, its life ends and Mojo destroys it. This is your chance to clean up what it owned. 🧹

Mojo calls a special method named __del__ to destroy a value. It runs automatically when the value goes out of scope.

Mojo destroys values at a predictable point, as soon as they are last used. There is no waiting on a garbage collector.

Mojo runs __del__ right after a value is last used, often before the block closes. This frees resources as early as possible.

If your type holds a heap buffer, __del__ is where you release it. Doing so prevents memory from leaking over time.

Inside __del__ the value is owned, so you can safely tear down its resources. After this, the value no longer exists.

For simple types you write nothing. Mojo synthesizes a destructor that cleans up each field in turn, so leaks are avoided.

Write your own __del__ when you manage a raw resource, like an allocation or file handle, that needs explicit release.

Each value is destroyed exactly once. Moves transfer ownership so only the final holder runs __del__, avoiding double frees.

Once __del__ completes, Mojo guarantees the value is gone. Its ownership rules stop you from touching freed data.

Deterministic destruction gives you C-like control with built-in safety. Cleanup is timely, predictable, and automatic.

Lets check destruction.

__del__ runs when a value’s life ends, deterministically and exactly once, letting you clean up safely without a GC. 🎯