Question

I have 5 files:

• ExecutionStrategyInterface.h
• ExecutorInterface.h
• TaskCollectionInterface.h
• TaskExecutor.h
• TaskExecutor.cpp.

TaskExecutor implements the following member method:

void TaskExecutor::execute(TaskCollectionInterface* tci, const ExecutionStrategyInterface& es) {
    es.execute(tci);
}

At compile time, the compiler calls a member method with a parameter of type pointer to a reference
(i.e: mylib::core::TaskCollectionInterface*&).

TaskExecutor.cpp: In member function ‘virtual void mylib::core::TaskExecutor::execute(mylib::core::TaskCollectionInterface*, const mylib::core::ExecutionStrategyInterface&)’:
TaskExecutor.cpp:16: error: no matching function for call to ‘mylib::core::ExecutionStrategyInterface::execute(mylib::core::TaskCollectionInterface*&) const’
./././ExecutionStrategyInterface.h:24: note: candidates are: virtual void mylib::core::ExecutionStrategyInterface::execute(TaskCollectionInterface*) const
make: *** [TaskExecutor.o] Error 1

Can anyone explain me what is happening here please ?

---

Classes:

ExecutionStrategyInterface.h

#ifndef _EXECUTIONSTRATEGYINTERFACE_H_
#define _EXECUTIONSTRATEGYINTERFACE_H_

class TaskCollectionInterface;

namespace mylib { namespace core {

/**
 *  Interface for executing a strategy.
 */
class ExecutionStrategyInterface {
 public:
    /**
     * Executes a strategy
     */
    virtual void execute(TaskCollectionInterface* tci) const = 0;
};

}} // namespaces

#endif // _EXECUTIONSTRATEGYINTERFACE_H_

TaskCollectionInterface.h

#ifndef _TASKCOLLECTIONINTERFACE_H_
#define _TASKCOLLECTIONINTERFACE_H_

#include "./ExecutionStrategyInterface.h"

namespace mylib { namespace core {

/**
 *  Interface for a collection of tasks.
 */
class TaskCollectionInterface {
 public:
    ~TaskCollectionInterface();
};

}} // namespaces

#endif // _TASKCOLLECTIONINTERFACE_H_

ExecutorInterface.h

#ifndef _EXECUTORINTERFACE_H_
#define _EXECUTORINTERFACE_H_

class ExecutionStrategyInterface;
class TaskCollectionInterface;

#include "./ExecutionStrategyInterface.h"
#include "./TaskCollectionInterface.h"

namespace mylib { namespace core {

/**
 *  Interface for an executor.
 */
class ExecutorInterface {
 public:
    virtual void execute(TaskCollectionInterface* tci, const ExecutionStrategyInterface& es) = 0;
    ~ExecutorInterface();
};

}} // namespaces

#endif // _EXECUTORINTERFACE_H_

TaskExecutor.h

#ifndef _TASKEXECUTOR_H_
#define _TASKEXECUTOR_H_

#include "./ExecutorInterface.h"

class TaskCollectionInterface;
class ExecutionStrategyInterface;

namespace mylib { namespace core {

/**
 *  Task Runner.
 */
class TaskExecutor: public ExecutorInterface {
 public:
    virtual void execute(TaskCollectionInterface* tci, const ExecutionStrategyInterface& es) = 0;
};

}} // namespaces

#endif // _TASKEXECUTOR_H_

TaskExecutor.cpp

#include "./TaskExecutor.h"
#include "./ExecutionStrategyInterface.h"
#include "./TaskCollectionInterface.h"

namespace mylib { namespace core {

void TaskExecutor::execute(TaskCollectionInterface* tci, const ExecutionStrategyInterface& es) {
    es.execute(tci);
}

}} // namespaces

Answer 1

This is confusing because you are forward-declaring the class outside the namespace, so you are ending up with two different classes with the same name. You’ll want something like this instead:

namespace mylib {
  namespace core {
    class TaskCollectionInterface;
    class ExecutionStrategyInterface {
      .
      .
      .
    };
  }
}

The way you have it now, your execute method is taking a pointer to ::TaskCollectionInterface instead of mylib::core::TaskCollectionInterface.