Exceptions.md

86 - Exceptions

Solidity uses state-reverting exceptions to handle errors. Such an exception undoes all changes made to the state in the current call (and all its sub-calls) and flags an error to the caller

1. When exceptions happen in a sub-call, they “bubble up” (i.e., exceptions are rethrown) automatically. Exceptions to this rule are send and the low-level functions call, delegatecall and staticcall: they return false as their first return value in case of an exception instead of “bubbling up”.

2. Exceptions in external calls can be caught with the try/catch statement

3. Exceptions can contain data that is passed back to the caller. This data consists of a 4-byte selector and subsequent ABI-encoded data. The selector is computed in the same way as a function selector, i.e., the first four bytes of the keccak256-hash of a function signature - in this case an error signature.

4. Solidity supports two error signatures: Error(string) and Panic(uint256). The first (“error”) is used for “regular” error conditions while the second (“panic”) is used for errors that should not be present in bug-free code.

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Slide Screenshot

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Slide Deck

• State-reverting Exceptions
• Sub-call Exception -> Bubble-up
• Except -> send/*call
• External Calls -> try/catch
• Caller -> Selector+Data
• Error(string) -> Regular
• Panic(uint256) -> Assertions

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References

• Youtube Reference

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Tags

System Operations,External Calls