core::traits::Destruct

A trait that allows for custom destruction behavior of a type. In Cairo, values must be explicitly handled - they cannot be silently dropped. Types can only go out of scope in two ways:

1. Implement Drop - for types that can be discarded trivially
2. Implement Destruct - for types that need cleanup when destroyed. Typically, any type that contains a Felt252Dict must implement Destruct, as the Felt252Dict needs to be “squashed” when going out of scope to ensure a program is sound.

Generally, Destruct does not need to be implemented manually. It can be derived from the Drop and Destruct implementations of the type’s fields.

Signature

pub trait Destruct

Examples

Here’s a simple type that wraps a Felt252Dict and needs to be destructed:

use core::dict::Felt252Dict;

// A struct containing a Felt252Dict must implement Destruct
#[derive(Destruct, Default)]
struct ResourceManager {
    resources: Felt252Dict,
    count: u32,
}

#[generate_trait]
impl ResourceManagerImpl of ResourceManagerTrait{
   fn add_resource(ref self: ResourceManager, resource_id: felt252, amount: u32){
       assert!(self.resources.get(resource_id) == 0, "Resource already exists");
       self.resources.insert(resource_id, amount);
       self.count += amount;
   }
}

let mut manager = Default::default();

// Add some resources
manager.add_resource(1, 100);

// When manager goes out of scope here, Destruct is automatically called,
// which ensures the dictionary is properly squashed

Trait functions

destruct

Signature

fn destruct(self: T)