How do you manipulate a storage struct array with an external library function?

Question

Basic pseudocode mockup of my problem

import libraryB;
contract A{
struct Person{
string Name;
uint age;
}
Person[] public Party;
Party[0] = (Alice, 30);
libraryB.addAgeToPerson(Party[0], 1)
}
library libraryB{
struct Person{
string Name;
uint age;
}
function addAgeToPerson(Person storage PersonToAddAgeTo, uint ageToAdd) external {
 PersonToAddAgeTo.age += ageToAdd;
}
}

Contract A is using a delegatecall unto the libraryB to use the function, passing the storage pointer to Person[] public Party; The struct is defined in both instances, but I get the error:

TypeError: Invalid type for argument in function call. Invalid implicit conversion from struct Contract A.Person storage ref to struct libraryB.Person storage pointer requested.

Any idea on how to pass a storage struct from a contract into a delegatecall to a Library to work with? I thought delegatecalls preserve the callers context..

Thanks for any input!

score 0 · Accepted Answer · answered Mar 31 '22 at 15:15

Inside Contract A , Person is actually A.Person while in libraryB Person is libraryB.Person when you do the delegate call you are giving a pointer to A.Person to the library that expects a storage pointer to libraryB.Person, hence the error.

Any idea on how to pass a storage struct from a contract into a delegatecall to a Library to work with?

Just define your struct inside your library as described in this answer and change all references to Person in contract A to libraryB.Person like this:

library libraryB {
struct Person{
    string Name;
    uint age;
}

function addAgeToPerson(Person storage PersonToAddAgeTo, uint ageToAdd) external {
    PersonToAddAgeTo.age += ageToAdd;
}


}
contract A {
libraryB.Person[] public Party;

constructor() {
    Party.push(libraryB.Person(&quot;Alice&quot;, 30));
    libraryB.addAgeToPerson(Party[0], 1);
}

}

How do you manipulate a storage struct array with an external library function?

1 Answers1