Cairo 1.0 Q&A #2267
Replies: 18 comments 37 replies
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Hi, Is it possible to execute bitwise operations on felts?. |
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I also have this question. I do not see any bitwise operations for felt yet. What is the effort to implement this? |
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Hi @drcapybara I think the reason is to motivate developers to use |
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I try to declare the official hello_starknet contract with command: And I get error: Maybe my starknet version is wrong? Or just the official contract does't work? starknet version: |
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When I update a mutable variable inside a break condition of a loop it throw an error. This is the code: and this is the error: This error is kind of odd, shouldn't this logic valid in Cairo1? |
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How to write code in Cairo that is similar to Rust's
use case: |
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In /// Generate getters and setters skeleton for a non-mapping member in the storage struct.
fn handle_legacy_mapping_storage_var(address: &str) -> String {
format!(
"
mod $storage_var_name$ {{$extra_uses$
use starknet::SyscallResultTrait;
use starknet::SyscallResultTraitImpl;
fn address(key: $key_type$) -> starknet::StorageBaseAddress {{
starknet::storage_base_address_from_felt252(
hash::LegacyHash::<$key_type$>::hash({address}, key))
}}
fn read(key: $key_type$) -> $value_type$ {{
// Only address_domain 0 is currently supported.
let address_domain = 0_u32;
starknet::StorageAccess::<$value_type$>::read(
address_domain,
address(key),
).unwrap_syscall()
}}
fn write(key: $key_type$, value: $value_type$) {{
// Only address_domain 0 is currently supported.
let address_domain = 0_u32;
starknet::StorageAccess::<$value_type$>::write(
address_domain,
address(key),
value,
).unwrap_syscall()
}}
}}"
)
}Note the line The result of the inner hash is in the |
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How can I generate from a cairo file the |
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how can i get current block number in cairo contract? Just like block.number in solidity |
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Hello! I'm currently utilizing the following crate: Here are my questions:
Thanks in advance for any clarification here! |
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First of all - you can probably consider just stating the value of the gas-builtin counter - it would indicate the actual amount of used gas in the counter - if you are actually trying to consider the gas mechanism, instead of the actual used resources. You need the data you requested only for the process of emulating the actual used resources using the gas mechanism. to answer the questions specifically:
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Thanks for the detailed answer @orizi. I'm currently building a solution that is based on the gas mechanism (if I understand it correctly) because I use Sierra and it's metadata in order to get the costs for specific functions/libfuncs and then while executing the program, to illustrate where and how much gas is consumed. If this is an acceptable approach, it could be really informative when it comes to illustrating how it works in Cairo in general. Some new questions that came to my mind after thinking about your answer:
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Hello! How can this be done? Here's an example: #[starknet::interface]
trait ITest<TContractState> {}
#[starknet::contract]
mod Test {
#[storage]
struct Storage {
byte_array: ByteArray
}
#[constructor]
fn constructor(ref self: ContractState, byte_array: ByteArray) {
self.byte_array.write(byte_array);
}
}
use starknet::ClassHash;
#[starknet::interface]
trait IFactory<TContractState> {
fn create_test(self: @TContractState, class_hash: ClassHash, byte_array: ByteArray);
}
#[starknet::contract]
mod Factory {
use starknet::syscalls::{deploy_syscall};
use starknet::ClassHash;
use starknet::SyscallResultTrait;
#[storage]
struct Storage {}
#[abi(embed_v0)]
impl Factory of super::IFactory<ContractState> {
fn create_test(self: @ContractState, class_hash: ClassHash, byte_array: ByteArray) {
let mut constructor_calldata: Array::<felt252> = array![];
constructor_calldata.append(byte_array.into()); // <-- here's the problem
// Trait has no implementation in context: core::traits::Into::<core::byte_array::ByteArray, core::felt252>.
let (deployed_address, _) = deploy_syscall(
class_hash, 0, constructor_calldata.span(), false
)
.unwrap_syscall();
}
}
} |
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the calldata is the serialization of all parameters for the constructor: |
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@orizi so that's another way to serialize data for the constructor, awesome. I used this approach in my own project and as soon as my tuple grows to 5+ elements, e.g.: let mut constructor_calldata: Array::<felt252> = array![];
(caller, title, target, duration, this).serialize(ref constructor_calldata);the compiler complains with: But when I remove any of the tuple members, the compiler error disappears. I even tried this with 5 elements of the same type, and got the same compiler error. This seems to be some hard cap on the maximum number of elements in a tuple that can be serialized. Is this expected behavior? |
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Yes, we have implementation for tuples of up to 4 elements. |
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🤯 So simple, yet magical. Thanks for the great and timely help! |
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Is there a way to get the current class hash inside a contract? Something like: #[starknet::interface]
trait ITest<TContractState> {
fn test(self: @TContractState);
}
#[starknet::contract]
mod Test {
use starknet::ClassHash;
#[storage]
struct Storage {}
fn test(self: @ContractState) {
let cur_class_hash: ClassHash = // what function to use to get the current contract's class hash??
}
} |
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ATM you can't. We want to add two small syscalls that will address this (you only need the first but listing both anyway):
This is coupled with Starknet support, and can only make it to Starknet >= 0.13.3, hence it won't be present in the next few months. |
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Thanks. |
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What is the most gas-efficient way to accumulate string concatenations in a loop? fn print_he_10000_times() {
let mut he_10000_times: ByteArray = "";
let mut n: u8 = 0;
while n < 10000 {
he_10000_times.append(@"he");
n += 1;
};
println!("{he_10000_times}");
}
fn main() {
print_he_10000_times();
}P.S. Unrelated, but if I change the |
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I have a very specific use-case - I'm creating a Cairo track on Exercism. One of the exercises I'm implementing requires the learner to concatenate a string a bunch of times to create the famous "99 Bottles of Beer" song. The exercise is supposed to help the learner practice using loops, if-statements and strings. |
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Oh, so efficiency isn't an issue? If so, the loop it totally fine, as it is just an example. |
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Yeah, in retrospect, I should've included this in my original message, it would have added some important context. I was wondering whether there exists some function or trait (or approach) that does this string concatenation more efficiently, so that I can include it in the solution explanation as a fun tip for the learner. |
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if you are extending an existing string, this is basically the best you can do for the time being. |
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Ok, thanks for being patient with me! |
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In general, this issue isn't really scalable, I suggest asking in the cairo discord, or the cairo questions tg group (the latter requires filling a form to show you're a real person). |
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TBH I think we could use a category on discussions and post each question as separate post. Kinda Stack-overflow like |
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Fixed-size arrays are available in Cairo, but I how can I use array-related function with them? E.g. for this code: fn main() {
let arr: [felt252; 2] = [1, 2];
let sp: Span<felt252> = arr.span();
}I get the following error: Does that mean fixed-size arrays are not yet fully supported in the language? |
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only |
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It's kind of confusing to be using a regular release (so not "nightly") and not have full features for a feature. |
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and destructuring. it was partially useful for some specific instances - just wasn't for the usage as array case. |
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I am trying to understand why the compiler is not able to infer the type of Example code: fn to_option(num: usize) -> Option<usize> {
if num > 10 {
Option::Some(num)
} else {
Option::None
}
}
fn from_option(opt_num: Option<usize>) -> usize {
if let Option::Some(num) = opt_num {
num
} else {
0
}
}
#[cfg(test)]
mod tests {
#[test]
fn test_to_option() {
let num: usize = 5;
assert_eq!(super::to_option(num), Option::None); // Type annotations needed. Failed to infer ?15
}
#[test]
fn test_from_option() {
assert_eq!(super::from_option(Option::None), 0); // this infers the Option::None type with no issues
}
}Why is the compiler able to infer the type of the |
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Thanks for finding this bug - will be fixed with the next release. |
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Glad to be of help! Will open an issue |
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you can - but was already solved on main - and should be released soon. |
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Oh, didn't realize that. Will close it then |
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Is there anything like a list of (Rust-like) features that are planned to be implemented for Cairo? I found the Cairo 0 parity roadmap, but that's not what I'm referring to; I'm talking about new traits, new syntax, new structs etc. |
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Hey guys! I am using scrab and cairo with version 2.6.3. I installed Cairo 1.0 plugin in my VSC, but the syntax highlighting seems not working properly. |
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Your file is named hello_world.cairo. Do you have a module with the same name defined in your /src/lib.cairo file? You need this for the compiler to know that hello_world.cairo is part of your project. This will also enable syntax highlighting. |
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Yes I have. I found that the language server seems not working properly. |
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please install VSCode extension manually from main and then follow these steps to debug your problem: https://github.com/starkware-libs/cairo/tree/main/vscode-cairo#troubleshooting on |
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I'm trying to understand smart pointers and how to use them to implement a doubly linked list. When I have two boxes See the below example: type List<T> = Option<Box<Node<T>>>;
#[derive(Drop, Copy, Debug)]
struct Node<T> {
data: T,
next: List<T>,
previous: List<T>
}
#[derive(Drop, Copy, Debug)]
struct DoublyLinkedList<T> {
head: List<T>,
tail: List<T>,
len: usize,
}
#[generate_trait]
impl DoublyLinkedListImpl<T, +Drop<T>, +core::fmt::Debug<T>, +Copy<T>> of DoublyLinkedListTrait<T> {
fn new() -> DoublyLinkedList<T> {
DoublyLinkedList { head: Option::None, tail: Option::None, len: 0 }
}
fn push(ref self: DoublyLinkedList<T>, data: T) {
match self.tail {
Option::None => {
let node = BoxTrait::new(Node { data, next: Option::None, previous: Option::None });
self.tail = Option::Some(node);
// head & tail should now point to the same node
self.head = self.tail;
self.len += 1;
},
Option::Some(tail) => {
let node = BoxTrait::new(
Node { data, next: Option::None, previous: Option::Some(tail) }
);
let mut tail = tail.unbox();
// Here's the problem! Since both head & tail point to the same node,
// I would expect the below assignment to update *both* of the boxes
// **But only `tail` gets updated!!!** (see below printlns)
tail.next = Option::Some(node);
self.tail = tail.next;
self.len += 1;
},
}
}
}
fn main() {
let mut list = DoublyLinkedListTrait::<u32>::new();
println!("init");
println!("head: {:?}", list.head); // Option::None(())
println!("tail: {:?}\n", list.tail); // Option::None(())
list.push(23);
println!("push(23)");
println!("head: {:?}", list.head); // Option::Some(&Node { data: 23, next: Option::None(()), previous: Option::None(()) })
println!("tail: {:?}\n", list.tail); // Option::Some(&Node { data: 23, next: Option::None(()), previous: Option::None(()) })
list.push(5);
println!("push(5)");
println!("head: {:?}", list.head); // Option::Some(&Node { data: 23, next: Option::None(()), previous: Option::None(()) })
println!("tail: {:?}\n", list.tail); // Option::Some(&Node { data: 5, next: Option::None(()), previous: Option::Some(&Node { data: 23, next: Option::None(()), previous: Option::None(()) }) })
}Why does this behavior occur? Also I would really appreciate an explanation on how to accomplish this the correct Cairo way. |
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The initial issue with this approach is the fact that Cairo's memory is immutable. |
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Thanks for the clarification! I figured it had something to do with memory immutability. |
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For anyone facing a similar issue, I used the following structure to simulate a doubly linked list: use core::dict::Felt252Dict;
type Index = Option<felt252>;
struct DoublyLinkedList<T> {
dict: Felt252Dict<Nullable<Node<T>>>,
head: Index,
tail: Index,
len: usize,
next_index: felt252,
}
#[derive(Drop, Copy)]
struct Node<T> {
station: T,
next: Index,
previous: Index
} |
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Is there a way to compile and run a Cairo file without the use of Scarb? For context, in Rust I can create a main.rs file and run it with |
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This would be a nice-to-have feature, nothing too important |
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if you use no dependencies (so scarb isn't used): |
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Ask all your questions about Cairo 1.0
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