#13508: Clarify Some Restrictions on Compact Regions -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: ezyang Type: bug | Status: patch Priority: lowest | Milestone: 8.2.1 Component: | Version: 8.1 libraries/compact | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3407 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: new => patch * differential: => Phab:D3407 * milestone: => 8.2.1 Comment: I believe mutable byte arrays should be fine. The limitation is merely that you can't have things with **mutable pointers**. This limitation is due to the principle invariant of a compact region: that all objects in the transitive closure of an given member must also be members of the region. This invariant is enforced when the region is constructed. Allowing mutable pointers (e.g. `MutableArray#` and `MutVar#`) would enable the user to break this invariant by introducing a pointer to an object residing outside of the region. I agree that the language in the documentation could be improved. How does Phab:D2407 look? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13508#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler