Skip to main content
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)