Read a Cairo array without consuming its first element
Cairo arrays support appending and popping from the front. A parser that calls pop_front while merely peeking advances the queue for every later consumer.
Choose reading or consuming explicitly
For the example, pop_front removes ten from the logical queue. If a validator needs only to inspect the first item, use the available indexed or span snapshot accessors and handle the empty case before consuming anything.
queue before pop: [10, 20, 30]
pop_front(): 10
queue after pop: [20, 30]
Test the parser with two consecutive reads of the same input and then an intentional pop. The reads should observe ten, while the next item after the pop should be twenty. An optional accessor can represent an empty or out-of-range lookup.
Rebuild data when replacing an element
Cairo execution memory is immutable once written. A normal Array does not provide arbitrary in-place replacement like a mutable vector in some host languages. Construct a new sequence or choose a dictionary when the algorithm genuinely needs updates by key. starknet.io The Cairo Programming Language