Type Narrow Issue

Question

I have tried a sample Ballerina code below.

type RecordSample record {|
    int x;
|};

class testClass {
    RecordSample|error sampleVariable;

    function init() {
        self.sampleVariable = test();
    }

    function methodA() {
        self.init()
        if self.sampleVariable is error {
            return self.sampleVariable.message();
        }
    }
}

function test() returns RecordSample|error {
    if 1> 2 {
        return {x: 1};
    } else {
        return error("Error");
    }
}

I am getting an error as it do not Narrow type in line self.sampleVariable.message(); May i know the reason for this error ? (Error Message is undefined function 'message' in type )

Answer 1

Type is narrowed only for local variables and parameters - basically, where it can be guaranteed that the narrowed type will hold. Assigning to a local variable and doing the is check will narrow the type of the variable.

RecordSample|error sampleVariable = self.sampleVariable;
if sampleVariable is error {
    return sampleVariable.message();
}