Why doesn't this try/catch block catch the revert in `asset.symbol`?

Question

I wrote this Solidity function:

function getAssetSymbol(IERC20Metadata asset) internal view returns (string memory) {
    try asset.symbol() returns (string memory symbol) {
        return symbol;
    } catch {
        return "ERC20";
    }
}

And, while testing it, I realized that reverts are not caught when:

• asset is an address that doesn't contain code
• asset returns a bytes32 instead of string (e.g. the MKR token does this)

Why is that? I was expecting try/ catch to handle these reverts.

Answer 1

try..catch doesn't catch the boundary exceptions, just the inner method call. Exactly that, what you have mentioned:

• checks if address is not void
• checks if extcodesize exists
• --checks if method exists-- This will be caught.

Any fails at this steps cause the revert. After the method is executed:

• checks if the return is as expected and can be decoded

A failure at this step also causes the revert.

Additional infos: try-catch

---

Sorry, initially I've written it reverts if the method does not exist. I was not sure about that and I was wrong, the call to an unexisting method will be caught. I think the method invocation is already at the inner contract level, as it executes a fallback method if any, otherwise reverts, which will be caught by the try..catch