#4149: Make Permissions type abstract
------------------------------------+---------------------------------------
Reporter: igloo | Owner:
Type: proposal | Status: new
Priority: normal | Milestone: Not GHC
Component: libraries/directory | Version: 6.12.3
Keywords: | Difficulty:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
------------------------------------+---------------------------------------
The `Permissions` type in `System.Directory` aims to be a lowest-common-
denominator type. This makes it unsuitable for some tasks. For example, a
`copyPermissions` primitive had to be implemented, as it is not possible
to use the `getPermissions` and `setPermissions` functions to copy the
permissions from one file to another:
{{{
$ ls -l foo*
-rwxr-x-wx 1 ian ian 0 Jun 23 21:27 foo1
---------- 1 ian ian 0 Jun 23 21:27 foo2
---------- 1 ian ian 0 Jun 23 21:27 foo3
$ hd -e 'System.Directory.copyPermissions "foo1" "foo2"'
$ hd -e 'System.Directory.getPermissions "foo1" >>=
System.Directory.setPermissions "foo3"'
$ ls -l foo*
-rwxr-x-wx 1 ian ian 0 Jun 23 21:27 foo1
-rwxr-x-wx 1 ian ian 0 Jun 23 21:27 foo2
-rwx------ 1 ian ian 0 Jun 23 21:27 foo3
}}}
I think we would be better served by the `Permissions` type being abstract
in `System.Directory`, with the `unix` and `Win32` packages providing the
real definition, and some system-specific functions on it. This would
allow the generic get/set functions to implement `copyPermissions`.
This proposal just does the step which has most potential to cause
problems for packages that use the type: It makes the type abstract in
`System.Directory` (and adds explicit setter functions, so no
functionality is lost).
The type is also exported in Haskell 98's `Directory` module. I think this
should get its own copy of the type.
Suggested discussion deadline: 9 July 2010.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4149>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
