check if object exists before borrow

[dancespiele]

Discord user ID

spielcrypto

Describe your question in detail.

I have this view function:

#[view]
public fun get_balance_to_claim(account_addr: address): u64 acquires FeesToClaim {
    let fees_to_claim = borrow_global<FeesToClaim>(account_addr);
    fees_to_claim.amount
}

I think if FeesToClaim object is not created for that account address, it will fail but I don't know how can I check if object exists for that account because I cannot find any borrow_option

What error, if any, are you getting?

No response

What have you tried or looked at? Or how can we reproduce the error?

No response

Which operating system are you using?

Linux (Ubuntu, Fedora, Windows WSL, etc.)

Which SDK or tool are you using? (if any)

Aptos CLI

Describe your environment or tooling in detail

No response

[gregnazario]

This is a very common pattern with the resource functions. You can use exists<>. This does bring a good point though, probably something that could be good to add a borrow_option or borrow_with_default function

module 0x42::example {
  #[view]
  public fun get_balance_to_claim(account_addr: address): Option<u64> acquires FeesToClaim {
      if (exists<FeesToClaim>(account_addr) {
          let fees_to_claim = borrow_global<FeesToClaim>(account_addr);
          option::some(fees_to_claim.amount)
      } else {
          option::none()
      }
  }
}