Type error, option pattern cannot consume expected type async<$List> (?Company)

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1

Hi everyone!

I have 2 files one is database.mo and other is main.mo. I tried to follow linkedup logic.

database.mo:

public func listCompanies(userid: Principal): async ?Company {
    if(isStudent(userid)){
        func isEq(company: Company): Bool {
            company.owner == userid;
        };

        switch (Array.find<Company>(personalList, isEq)) {
            case(null) {
                 return null;
            };
            case(?exists) {
                return ?{
                    id = exists.id;
                    owner = exists.owner;
                    companyID = exists.companyID;
                };
            };
        };
    } else {return null;}
};

main.mo:

public shared(msg) func List(): async ?Company{
directory.listCompanies(msg.caller);
};

I tried to do something like this in main.mo file because I had some errors:

public shared(msg) func List(): async ?Company{
   switch (directory.listCompanies(msg.caller))
    {
        case(?e){
            return ?{
            
            };
        };
    };
};

The error appears with the second try that I wrote above, and is this:

type error, option pattern cannot consume expected type
  async<$List> (?Company)

What I have to do to solve this error? where is my mistake?

Thank you!

2

You probably don’t want listCompanies() to have an async return in database.mo, so the first line there should be:

public func listCompanies(userid: Principal): ?Company {

1 Like
3

You use async methods in your main.mo actor because that’s your canister’s interface on the IC and it needs to be called asynchronously, but your database.mo is probably a module within your canister? In which case it doesn’t need this.

If listCompanies were async, you would need to await the return value in the switch statement:

switch (await directory.listCompanies(msg.caller))

3 Likes
4

Thank you for your answer and for your willing to help! :smiley: These answers helped me a lot!

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