Lesson 7: FundMe__NotOwner(); is nowhere defined

[ManuWeb3]

Hi everyone,

error code: error FundMe__NotOwner(); is nowhere defined in FundMe.sol. I mean it's body / definition is not coded.

And, we're able to directly use it in the modifier onlyOwner and it does revert when expected. Just got it unit tested in FundMe.test.js as well.

Is it some standard error code in Solidity which is not needed to be custom-defined by us?

Thanks

[Muhammad-Abdullah012]

No, it is not standard error code,
you can use anything,..

error yourName();
error WhatIsThis();

And you'll be able to directly use it,...

[krakxn]

When do you get that error? Whilst deploying?

[ManuWeb3]

No, Patrick told this while refactoring the code regarding storage of the strings and gas optimisation.
So, I was just wondering that it's body (string message to be displayed, etc.) is nowhere defined unlike actual require ( ) clause.

[krakxn]

Custom errors are gas-efficient as they do not involve the creation of a string as in the case with require.

Good read on custom-errors: Link to Solidity article

FAQ:

Can we custom name them? Yes
Does it need a body? No, we do it simply by a revert

Note: It is essentially just a error which we can custom-name by ourselves, hence it should be used appropriately and not in wrong places else you will be confused, EG: Error A should be placed in Function A, and not in Function B

Hope this helps!

[ManuWeb3]

Yes, it did. Thanks @krakxn for shring this link, going through it.

[alymurtazamemon]

@ManuWeb3 This is how it works it does not need a body, just declaration and reverts where needed.