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

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