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digitalmars.D.learn - task! with a static template method gives "null this"

reply Lee Braiden <leebraid gmail.com> writes:
Hi all,

I'm defining a template class with a static method, and adding a call to 
that to a taskpool.  However, when I run it, I get a "null this" error 
from parallelism.d.

Here's the minimised code:

class Population(GeneType)
{
	alias Population!(GeneType) ThisType;

	static void breedIndividual(ThisType oldPop, ThisType newPop)
	{
		auto mom = oldPop.selectParent();
		auto pop = oldPop.selectParent();

		auto kid = mom.crossbreedFrom(pop);

		// chance of mutation
		if (uniform(0, MUTATION_CHANCE) == 0)
		{
		    auto oldFitness = kid.fitness();
		    kid.dna.mutate();
		    auto newFitness = kid.fitness();
		}

		newPop.lifeforms_ ~= kid;
	}

	ThisType evolve(TaskPool p)
	{
		...

		auto t = task!breedIndividual(this, newPop)

		...
	}
}


The actual error message is:

core.exception.AssertError /usr/include/d2/4.6/std/parallelism.d(2723): 
null this


There is no "this" usage that I can see, in the breedIndividual() 
(static) method... EXCEPT maybe for the fact that ThisType depends on the 
template class expansion.  But that's all expanded at compile-time, and 
doesn't matter, right?

So I'm not sure how to solve this.  My first thought was to move 
breedIndividual out of the class, but it does depend on ThisType, as 
defined in the class template.


Am I right that this is what's causing the "null this" error?  If so, 
what can I do to fix it?



Thanks,


-- 
Lee
Feb 23 2013
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 02/23/2013 03:23 PM, Lee Braiden wrote:

 Hi all,

 I'm defining a template class with a static method, and adding a call to
 that to a taskpool.  However, when I run it, I get a "null this" error
 from parallelism.d.

 Here's the minimised code:

 class Population(GeneType)
 {
 	alias Population!(GeneType) ThisType;

 	static void breedIndividual(ThisType oldPop, ThisType newPop)
 	{
 		auto mom = oldPop.selectParent();
 		auto pop = oldPop.selectParent();

 		auto kid = mom.crossbreedFrom(pop);

 		// chance of mutation
 		if (uniform(0, MUTATION_CHANCE) == 0)
 		{
 		    auto oldFitness = kid.fitness();
 		    kid.dna.mutate();
 		    auto newFitness = kid.fitness();
 		}

 		newPop.lifeforms_ ~= kid;
 	}

 	ThisType evolve(TaskPool p)
 	{
 		...

 		auto t = task!breedIndividual(this, newPop)

 		...
 	}
 }


 The actual error message is:

 core.exception.AssertError /usr/include/d2/4.6/std/parallelism.d(2723):
 null this


 There is no "this" usage that I can see, in the breedIndividual()
 (static) method... EXCEPT maybe for the fact that ThisType depends on the
 template class expansion.  But that's all expanded at compile-time, and
 doesn't matter, right?

 So I'm not sure how to solve this.  My first thought was to move
 breedIndividual out of the class, but it does depend on ThisType, as
 defined in the class template.


 Am I right that this is what's causing the "null this" error?  If so,
 what can I do to fix it?



 Thanks,


The following is minimized code, which does not have any compilation errors:

import std.parallelism;
import std.random;

enum mutationChance = 1000;
alias MUTATION_CHANCE = mutationChance;

class Population(GeneType)
{
     alias Population!(GeneType) ThisType;

     static void breedIndividual(ThisType oldPop, ThisType newPop)
     {
         auto mom = oldPop.selectParent();
         auto pop = oldPop.selectParent();

         auto kid = mom.crossbreedFrom(pop);

         // chance of mutation
         if (uniform(0, MUTATION_CHANCE) == 0)
         {
             auto oldFitness = kid.fitness();
             kid.dna.mutate();
             auto newFitness = kid.fitness();
         }

         newPop.lifeforms_ ~= kid;
     }

     ThisType evolve(TaskPool p)
     {
         // ...

         auto newPop = new ThisType;
         auto t = task!breedIndividual(this, newPop);

         // ...

         return new ThisType;
     }

     ThisType selectParent()
     {
         return new ThisType;
     }

     ThisType crossbreedFrom(ThisType)
     {
         return new ThisType;
     }

     int fitness()
     {
         return 42;
     }

     struct Dna
     {
         void mutate()
         {}
     }

     Dna dna()
     {
         return Dna();
     }

     ThisType[] lifeforms_;
}

void main()
{
     auto p = new Population!int;
}

You can replace my stub functions with your code to help identify the 
problem.

Ali
Feb 23 2013
parent Lee Braiden <leebraid gmail.com> writes:
On Sat, 23 Feb 2013 17:09:06 -0800, Ali Çehreli wrote:

 The following is minimized code, which does not have any compilation
 errors:
 
 [snip]
 
 You can replace my stub functions with your code to help identify the
 problem.
 
 Ali


Thanks Ali; much appreciated.


-- 
Lee
Feb 23 2013