Unable to compare union type (Float? | Integer?)

[steowens]

So far I can find no way to build a compare function which accepts a class which has a value of type (Float? | Integer?).

For example:

shared default actual Comparison compare(Number other){
        if(!(other.val exists)&&!(val exists)){
            return equal;
        } else if(val exists && !(other.val exists)){
            return larger;
        } else if(!(val exists) && other.val exists){
            return smaller;
        } else {
           if(val is Float){
               if(other.val is Float){
                  // Generates compiler error
                  // Specified expression must be assignable to declared type of ov:
                  //        Integer?|Float? (Null|Integer|Float) is not assignable to Float
                   Float ov = other.val;

                  // Generates compiler error
                  // Incorrect syntax: missing statement-ending ; at other expecting statement-ending ;
                  Float ov2 = (Float) other.val;

                   // Generates compiler error
                  // Operand expressions must be comparable: 
                  //   Integer?|Float? (Null|Integer|Float) is not a subtype of Comparable 
                  return val <=> other.val;
               }
           }

        }

    }

Even though the above code tests the type of val and other.val and asserts them to be the same, it is impossible ot cast or compare the two values.

[thradec]

Did you try type narrowing? In your example ...

if( is Float f = val, is Float f2 = other.val ) {
    return f <=> f2;
}

[gavinking]

Hi, @steowens, the syntax other.val is Float does not perform type narrowing, it is just a plain expression of type Boolean. What you would need is an is condition, as shown above by @thradec.

Also the syntax (Float) other.val is simply not legal Ceylon. That is a Java/C typecast, which does not exist in Ceylon.

You can find more information about this syntax here, here, and here.

I'm closing this issue since it's not a bug in Ceylon.

[steowens]

Thank you. Just saw your question and response. I am unfamiliar with Ceylon and was evaluating the language. Had the issue type been available I would have selected (question) as the issue type. Do you have a publicly accessible forum which we could use to ask such questions?

[DiegoCoronel]

@steowens you can try both:

• https://gitter.im/ceylon/user
• https://groups.google.com/forum/#!forum/ceylon-users

I believe those are enough to start.. but theres also dev chat and forum

[steowens]

Thank you. I didn't see those mentioned in your README.md file, nor on your Wiki. It might be a nice bit of info to include in your github site. I am sure I am not the only person who will be interested in learning where to go to ask questions.