Wat?

Yesterday, Seth Ladd posted a link to a humorous video which highlights a few WAT?!?! moments in Javascript and Ruby. He then discussed how Dart deals with some of these moments in Javascript WAT moments and Dart. Please watch the video and read Seth's blog prior to reading.

There are WAT moments in virtually every language. A line from the video says something along the lines of So since it is the plus operator, we can expect the same result if we switch the operands around.. In the case of the video it was discussing how Javascript handles adding an array and a hash, and a hash and an array. However this reminded me of the issue I ran into myself already in experimenting with Dart. Look at the following code:

main() {
  print("wat" + 1);
  print(1 + "wat");
}

What is particularly interesting is running this example in the variety of locations. First lets run it from the Dartboard, without checked mode. We get the result:

wat1
1wat

More or less what you'd expect to get adding a string and a number. We do see a little warning off to the side indicating String is not assignable to num. But being not in checked mode it does run and because its Dartboard it falls back to the Javascript implementation of number + string. Well lets see what we'll get in the DartVM...

wat1
Unhandled exception:
NoSuchMethodException - receiver: 'wat' function name: 'addFromInteger' arguments: [1]]
 0. Function: 'Object.noSuchMethod' url: 'bootstrap' line:360 col:3
 1. Function: 'IntegerImplementation.+' url: 'bootstrap_impl' line:1469 col:32
 2. Function: '::main' url: '/home/mbutler/dart/Test/Test.dart' line:3 col:11

Err WAT? Even more, that runtime error is.. far from clear on just what exactly is going on. Additionally in the VM we do get the same warning as stated above, on the line with the issue so that helps to track it down easy enough. Well lets go back to the dartboard and enable checked_mode:

wat1
Failed type check: type String is not assignable to type Number

Well that's kind of a reasonable error. Must get the same in the Dart VM using the 'enable_type_checks' flag.

wat1
Unhandled exception:
'bootstrap_impl': Failed type check: line 1468 pos 22: type 'OneByteString' is not assignable to type 'num' of 'other'.
 0. Function: 'IntegerImplementation.+' url: 'bootstrap_impl' line:1468 col:22
 1. Function: '::main' url: '/home/mbutler/dart/Test/Test.dart' line:3 col:11

Okay WAT? That error is almost as long as the first one but its a little more obscure I think. I see from the very last line of the error where the issue is in my code (I notice this now in the first error as well. I'm so used to seeing my code point at the top of the error with subsequent library calls following after that, that I didn't realize to look at the bottom of the error for my error). But the error itself is interesting "OneByteString" is not assignable to type "num" of "other"...? Of other what? String not assignable to num is understandable though not necessarily expected. But of other? I'm not sure. Just rambling a little bit at this point as well as I procrastinate getting some work done in the office today.

I'll post again later today if I get the opportunity as Seth has a couple of other blog posts written that I want to follow up on. Particularly on his one about 'this'.