Doppelganger | Smart contract mocking tool | Cryptocurrency library

The main issue with the bizarro pipe is that it creates hidden side-effects and makes it easier to create subtle bugs. It decreases code maintainability.

The issue, of course, is the persistent existence of . makes it all too easy to accidentally refer to this value later down the line: its presence masks mistakes if you at some point “forget” to assign to it and think you did. It’s easy to dismiss this possibility but such errors are fairly common and, worse, very non-obvious: you won’t get an error message, you’ll just get a wrong result. By contrast, if you forget the pipe symbol somewhere, you’ll get an immediate error message.

Worse, the bizarro pipe hides this error-prone side-effect in two different ways. First, because it makes the assignment non-obvious. I’ve argued previously that -> assignment shouldn’t be used since it hides a side-effect, and side-effects should be made syntactically obvious (the side-effect here is assignment, and it should happen where it’s immediately spotted: in the first column of the expression, not hidden away at its end). This is a fundamental objection to the use of -> (or any other attempt to mask side-effects), not limited to the bizarro pipe.

And because . is by default hidden (from ls and from the inspector pane in IDEs), this makes it even easier to accidentally depend on it.

Therefore, if you want to assign to a value instead of using a pipe, just do that. But:

1. Perform right-to-left assignment, i.e. use name = value or name <- value, not value -> name.
2. Use a descriptive name.

I can’t stress enough that this is an actual source of subtle bugs — don’t underestimate it!

Another issue is that its use breaks editor support for auto-formatting code. This is a “solvable issue” in some IDEs via plugins but the solution, as it were, solves an issue that should not even exist. To clarify what I mean, if you’re using the bizarro pipe you’d presumably want a hanging indent, i.e. something along these lines: