Guards are not Suited for the Above Principle

• E.g. in pidgen-Java (Doug Lea), ...

  Interface BoundedBuffer {
    WHEN(count > MIN) ACCEPT int get() { ... }
    WHEN(count < MAX) ACCEPT int put() { ... }
  }
  

  But "count < MIN" belongs to implementation!
• Other (minor?) drawbacks:
  • Guard re-evaluation timings.
  • Guard evaluation context.