How do I call a function into a contract with solidity and want to continue execution even if this call reverts?

Question

I have looked into the Solidity docs but cannot seem to find this feature. I want to call into a contract and want to push two values onto the stack: the actual return value AND if the execution completed or not (in the sense that a CALL-like opcode puts 0 on the stack).

The only way it seems to be doable is writing inline assembly, but this gets rather tough if the function I am calling is returning a dynamic sized bytes variable. I know that it is possible, of course, but I find it rather surprising that solidity does not have this feature.

Answer 1

When reading the solidity docs suddenly came across to the answer of "why is this not a feature yet". It will be in Solidity 0.5.0!

https://solidity.readthedocs.io/en/develop/050-breaking-changes.html

Functions .call(), .delegatecall() and .staticcall() now return (bool, bytes memory) to provide access to the return data.

Answer 2

It is required to clarify: “execution completed or not” is not unique.

Case 1: your execution fails because somewhere a revert or throw fires. In this case you cannot have any return from EVM (any) except a string optionally inserted in the reverting line, as per:

require (user != owner, “the cited string”);

but it is quite impossible to use it as return value in a smart contract in the sense you mean, but anyway something comes out from the reverting transaction.

Case 2: your execution fails because some of your checks or call return success=“false” or similar. This can be returned without any hassle in an obvious way, by means of return statement.

Hoping this can help.