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@SeanTAllen SeanTAllen released this 19 Aug 14:38

Pony 0.18.0 contains a high priority compiler bug fix. We recommend updating as soon as possible. Note, however, that there is a small breaking change in this release as well. It should be a quick upgrade if you are impacted.

Fix compiler crash on union-of-tuples to tuple conversions

Previously, when trying to compile a union-of-tuples, the compiler would segfault. Very annoying if you had a reasonable program like:

primitive Add
primitive Dec
type AddOrDec is (Add | Dec)
type CmRDTCounterOp is (AddOrDec, U128)

class CmRDTCounter
  var _value: U128

  new create() => _value = 0

  fun read(): U128 =>

  fun ref add(number: U128): CmRDTCounterOp =>
    let op: CmRDTCounterOp =
      if number >= 0 then
        (Add, number)
        (Dec, number)

  fun ref apply(op: CmRDTCounterOp) =>
    match op
      | (Add, let number: U128) => _value = _value + number
      | (Dec, let number: U128) => _value = _value - number

actor Main
  new create(env: Env) =>
    var counter = CmRDTCounter.create()
    let op1 = counter.add(10)

If you are interested in learning more, we suggest checking out issue #1513 for a bit more background and listen to the August 16, 2017, Pony development sync call where we discussed it in depth.

Change String.join to take Iterable

0.18.0 includes the implementation of RFC #48. It's a nice improvement to the usability of String.join. It is also, sadly, a breaking change. Such is life. Sometimes you break things to improve them. Upgrading should be straightforward.

Where you previously called "_".join(["zomg"]), you would now call "_".join(["zomg"].values()). Any place you hit a compiler error related to String.join, add a .values() to the ReadSeq you are passing and everything will work.

[0.18.0] - 2017-08-19


  • Fix compiler crash on union-of-tuples to tuple conversions (PR #2176)
  • Fix compiler error on lambda capture of '_' (PR #2171)
  • Fix read past the end of a buffer in pool.c. (PR #2139)


  • Make actor continuations a build time option (PR #2179)
  • RFC #48 Change String.join to take Iterable (PR #2159)
  • Change fallback linker to "gcc" from "gcc-6" on Linux. (PR #2166)
  • Change the signature of pony_continuation and pony_triggergc to take a pony_ctx_t* instead of a pony_actor_t*.