How to "unwrap" union types?

[tutiplain]

Hi all,

I am new to Ballerina, so please excuse me if this has been asked somewhere before, but at least I can't find a way to do it in the official docs. If I have a float|error type variable, I cannot use it in math operations. So far, what I've been doing is something like this:

float|error myFloat= getFloatSomehow(); float myRealFloat; if myFloat is error { //print some output } else { myRealFloat = myFloat; }

It seems wasteful to have a variable declared just for that. Is there a simpler way to do this?

[SandaruJayawardana]

Hi @tutiplain,
Math operations are not allowed with error types. So you have to ensure that the variable myFloat doesn't contain an error value before using it for math operations. IMO you can do it using either type narrowing or checking expressions.

float|error myFloat = 12;
    
if myFloat !is error { // using type narrowing
    myFloat = myFloat * 12;
}

public function main() returns error? {
    float|error myFloat = 12;
    myFloat = 12 * (check myFloat); // using check-expr
}

Does this solve your problem?

[SandaruJayawardana]

For general cases, I think you can use type-narrowing feature to unwrap union types.

[tutiplain]

Hi, thanks for your replies. I hadn't learned about check expressions yet. I used a function returning a float|error and using check expressions as in the example above to simplify my code a bit. At least now I don't have two variables, a float and a float|error, in my code.

[SandaruJayawardana]

FYI, You can use ballerina slack channel also to find answers to your questions, get support or learn how others are using Ballerina. https://ballerina.io/community/#ballerina-slack-community