• Marek Janukowicz (49/49) Aug 07 2015 This program works fine:
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (10/39) Aug 07 2015 Yes, it is a bug. The reason the number of members makes a difference is...

Marek Janukowicz <marek janukowicz.net> writes:

This program works fine:

import std.concurrency;

struct A {
  string a,b;
}

void main () {
  immutable A a = immutable A( "blah" ); 
  send( thisTid, a );
}

But if change struct A declaration to:

struct A {
  string a,b,c;
}

I get this error during compilation:
/opt/dmd2/linux/bin64/../../src/phobos/std/variant.d(653): Error: cannot 
modify immutable expression *p
/opt/dmd2/linux/bin64/../../src/phobos/std/variant.d(580): Error: template 
instance std.variant.VariantN!32LU.VariantN.opAssign!(immutable(A)) error 
instantiating
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(117):        
instantiated from here: __ctor!(immutable(A))
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(628):        
instantiated from here: __ctor!(immutable(A))
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(618):        
instantiated from here: _send!(immutable(A))
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(594):        
instantiated from here: _send!(immutable(A))

Is this is a bug?



On a related note - sometimes when sending a shared struct I get a 
compilation error similar to this:

/opt/dmd2/linux/bin64/../../src/phobos/std/variant.d(638): Error: function 
core.stdc.string.memcpy (void* s1, const(void*) s2, ulong n) is not callable 
using argument types (ubyte[32]*, shared(Notification)*, ulong)
/opt/dmd2/linux/bin64/../../src/phobos/std/variant.d(580): Error: template 
instance std.variant.VariantN!32LU.VariantN.opAssign!(shared(Notification)) 
error instantiating
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(117):        
instantiated from here: __ctor!(shared(Notification))
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(628):        
instantiated from here: __ctor!(shared(Notification))
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(618):        
instantiated from here: _send!(shared(Notification))
/opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(594):        
instantiated from here: _send!(shared(Notification))

If I then add more fields to the struct (eg. dummy "string a,b") it compiles 
fine.

Is this another bug or am I missing something?


-- 
Marek Janukowicz

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 08/07/2015 03:24 PM, Marek Janukowicz wrote:> This program works fine:
 import std.concurrency;

 struct A {
    string a,b;
 }

 void main () {
    immutable A a = immutable A( "blah" );
    send( thisTid, a );
 }

 But if change struct A declaration to:

 struct A {
    string a,b,c;
 }

 I get this error during compilation:
 /opt/dmd2/linux/bin64/../../src/phobos/std/variant.d(653): Error: cannot
 modify immutable expression *p
 /opt/dmd2/linux/bin64/../../src/phobos/std/variant.d(580): Error: 

template
 instance std.variant.VariantN!32LU.VariantN.opAssign!(immutable(A)) error
 instantiating
 /opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(117):
 instantiated from here: __ctor!(immutable(A))
 /opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(628):
 instantiated from here: __ctor!(immutable(A))
 /opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(618):
 instantiated from here: _send!(immutable(A))
 /opt/dmd2/linux/bin64/../../src/phobos/std/concurrency.d(594):
 instantiated from here: _send!(immutable(A))

 Is this is a bug?

Yes, it is a bug. The reason the number of members makes a difference is 
that Variant's implementation does different things depending on T.sizeof:

 
https://github.com/D-Programming-Language/phobos/blob/master/std/variant.d#L608

 On a related note - sometimes when sending a shared struct I get a
 compilation error similar to this:

Variant has a number of open bugs. Unfortunately, Variant reduces the 
quality of std.concurrency as Variant is used as a catch-all type by 
that module.

Ali