fix: #87 (#89)

NethermindEth · Oct 5, 2023 · d9a3cac · d9a3cac
1 parent a8d000b
commit d9a3cac
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Showing 3 changed files with 6 additions and 13 deletions.
diff --git a/listings/ch01-advanced-concepts/struct_as_mapping_key/src/contract.cairo b/listings/ch01-advanced-concepts/struct_as_mapping_key/src/contract.cairo
@@ -1,13 +1,13 @@
 #[starknet::contract]
 mod PetRegistry {
- use poseidon::poseidon_hash_span;
+ use hash::{HashStateTrait, Hash};
 
  #[storage]
  struct Storage {
- registration_time: LegacyMap::<felt252, u64>,
+ registration_time: LegacyMap::<Pet, u64>,
  }
 
- #[derive(Copy, Drop, Serde)]
+ #[derive(Copy, Drop, Serde, Hash)]
  struct Pet {
  name: felt252,
  age: u8,
@@ -18,17 +18,11 @@ mod PetRegistry {
  #[generate_trait]
  impl PetRegistry of PetRegistryTrait {
  fn register_pet(ref self: ContractState, key: Pet, timestamp: u64) {
- let mut serialized: Array<felt252> = ArrayTrait::new();
- Serde::<Pet>::serialize(@key, ref serialized);
- let hashed_key = poseidon_hash_span(serialized.span());
- self.registration_time.write(hashed_key, timestamp);
+ self.registration_time.write(key, timestamp);
  }
 
  fn get_registration_date(self: @ContractState, key: Pet) -> u64 {
- let mut serialized: Array<felt252> = ArrayTrait::new();
- Serde::<Pet>::serialize(@key, ref serialized);
- let hashed_key = poseidon_hash_span(serialized.span());
- self.registration_time.read(hashed_key)
+ self.registration_time.read(key)
  }
  }
 }
diff --git a/listings/ch01-advanced-concepts/struct_as_mapping_key/src/test.cairo b/listings/ch01-advanced-concepts/struct_as_mapping_key/src/test.cairo
@@ -25,7 +25,6 @@ mod tests {
  let pet = Pet { name: 'Cute Labrador', age: 5, owner: 'Louis' };
 
  // Store a pet.
-
  contract.register_pet(pet, 1234);
 
  // Read the array.

diff --git a/src/ch01-03-struct-mapping-key.md b/src/ch01-03-struct-mapping-key.md
@@ -1,6 +1,6 @@
 # Structs as mapping keys
 
-It is currently impossible to use structs as mapping keys. However, a workaround consists in hashing the values of all the struct's fields, and use this hash as a key in the `LegacyMap` type.
+In order to use structs as mapping keys, you can use `#[derive(Hash)]` on the struct definition. This will automatically generate a hash function for the struct that can be used to represent the struct as a key in a `LegacyMap`.
 
 Consider the following example in which we would like to use an object of
 type `Pet` as a key in a `LegacyMap`. The `Pet` struct has three fields: `name`, `age` and `owner`. We consider that the combination of these three fields uniquely identifies a pet.