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A trait for indexing operations (container[index]) where the input type is mutated. This trait should be implemented when you want to implement indexing operations on a type that’s mutated by a read access. This is useful for any type depending on a Felt252Dict, where dictionary accesses are modifying the data structure itself. container[index] is syntactic sugar for container.index(index).

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Signature

pub trait Index

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Examples

The following example implements Index on a Stack type. This Stack is implemented based on a Felt252Dict, where dictionary accesses are modifying the dictionary itself. As such, we must implement the Index trait instead of the IndexView trait. 
use core::ops::Index;

#[derive(Destruct, Default)]
struct Stack {
    items: Felt252Dict,
    len: usize
}

#[generate_trait]
impl StackImpl of StackTrait {
    fn push(ref self: Stack, item: u128) {
        self.items.insert(self.len.into(), item);
        self.len += 1;
    }
}

impl StackIndex of Index {
     type Target = u128;

     fn index(ref self: Stack, index: usize) -> Self::Target {
         if index >= self.len {
             panic!("Index out of bounds");
         }
         self.items.get(index.into())
     }
 }

let mut stack: Stack = Default::default();
stack.push(1);
assert!(stack[0] == 1);

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Trait functions

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index

Performs the indexing (container[index]) operation.

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Panics

May panic if the index is out of bounds.

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Signature

fn index(ref self: C, index: I) -> IndexTarget

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Trait types

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Target

The returned type after indexing.

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Signature

type Target;