Re: Immutable Structs and std.concurrency

[Jakob Ovrum]

On Thursday, 19 April 2012 at 16:26:19 UTC, Timon Gehr wrote:
On 04/19/2012 03:27 PM, Russel Winder wrote:
The program:
        import std.concurrency ;
        import std.stdio ;

        /*immutable*/ struct X { int i ; }

        void printI ( ) {
          receive (
                   ( X x ) { writeln ( x.i ) ; }
                   ) ;
        }

        int main ( immutable string[] args ) {
          auto x = spawn (&  printI ) ;
          x.send ( X ( 3 ) ) ;
          return 0 ;
        }

behaves entirely as expected.  Taking the comments off the 
immutable
leads to:

core.exception.AssertError@/home/users/russel/lib.Linux.x86_64/DMD2/bin64/../../src/phobos/std/variant.d(286): 
X
----------------
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(_d_assert_msg+0x1f) 
[0x43f81f]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(long 
std.variant.VariantN!(32uL).VariantN.handler!(immutableStruct.X).handler(std.variant.VariantN!(32uL).VariantN.OpID, 
ubyte[32]*, void*).bool tryPutting(immutableStruct.X*, 
TypeInfo, void*)+0x7a) [0x43b0fa]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(long 
std.variant.VariantN!(32uL).VariantN.handler!(immutableStruct.X).handler(std.variant.VariantN!(32uL).VariantN.OpID, 
ubyte[32]*, void*)+0x103) [0x43ae03]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(@property 
immutableStruct.X 
std.variant.VariantN!(32uL).VariantN.get!(immutableStruct.X).get()+0x57) 
[0x434cf7]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(void 
std.concurrency.Message.map!(void 
function(immutableStruct.X)*).map(void 
function(immutableStruct.X)*)+0x46) [0x434c96]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(bool 
std.concurrency.MessageBox.get!(void 
function(immutableStruct.X)*).get(scope void 
function(immutableStruct.X)*).bool onStandardMsg(ref 
std.concurrency.Message)+0x2d) [0x434731]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(bool 
std.concurrency.MessageBox.get!(void 
function(immutableStruct.X)*).get(scope void 
function(immutableStruct.X)*).bool scan(ref 
std.concurrency.List!(std.concurrency.Message).List)+0xd3) 
[0x434a47]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(bool 
std.concurrency.MessageBox.get!(void 
function(immutableStruct.X)*).get(scope void 
function(immutableStruct.X)*)+0x15e) [0x434692]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(void 
std.concurrency.receive!(void 
function(immutableStruct.X)*).receive(void 
function(immutableStruct.X)*)+0x2e) [0x434526]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(void 
immutableStruct.printI()+0x13) [0x433d1b]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(_D3std11concurrency11__T6_spawnZ6_spawnFbPFZvZS3std11concurrency3Tid4execMFZv+0x3d) 
[0x43abb5]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(void 
core.thread.Thread.run()+0x2a) [0x449caa]
/tmp/.rdmd-1000/home/users/russel/Progs/OddsByLanguage/D/Odds/immutableStruct.d.EDDA68DBDAF917356C855298813D6CD2(thread_entryPoint+0xf3) 
[0x449a43]
----------------

I believe this is wrong on so many levels, but is it because I 
don't
know D?


It certainly should work. std.concurrency does not do a good 
job dealing with head-immutable/head-const types currently 
(this includes class references). This needs to be fixed. The 
general problem is that it should be possible to declare a 
rebindable tail-immutable version of some type. 
std.typecons.Rebindable can be used for this, but an 
in-language solution would be superior.

Fixing std.concurrency entails fixing std.variant which entails 
fixing std.typecons.Rebindable by moving its functionality into 
the language where it belongs.

    https://github.com/D-Programming-Language/dmd/pull/3

This one has been lurking around forever, I wish Walter would 
accept this patch already.