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unused_return_value_monitor Class Template Reference

Return value adaptor for monitoring whether return values are used. More...

#include <stlsoft_unused_return_value_monitor.h>

List of all members.

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Detailed Description

template<typename V, typename M, typename R = V>
class stlsoft::unused_return_value_monitor< V, M, R >

Return value adaptor for monitoring whether return values are used.

Parameters:

V	The value type. This is the type that is to be returned by the function whose return type is to be monitored
M	The monitor function type. If the return value is not used, the monitor function instance will be called.
R	The reference type. This is the reference type, used in the constructor of the monitor, and the type of the member variable storing the value

If the value type is a simple type, you can just allow the reference type R to be defaulted, as in:

struct int_monitor
{
public:
void operator ()(void const *instance, int value) const
{
printf("Unused return value %d from object instance %p\n", value, instance);
}
};

class X
{
public:
  unused_return_value_monitor<int, int_monitor> fn()
  {
    return 10; // A copy is taken, but copies of ints usually cost the same as references to ints
  }
};




Where the return type is a complex type, you can make efficiency savings by using a (C++) reference for the reference type. However, this must only be done when the returned value will persist for the duration of the calling expression.

struct string_monitor
{
public:
  void operator ()(void const *instance, string const &value) const
  {
    printf("Unused return value %s from object instance %p\n", value.c_str(), instance);
  }
};

class Y1
{
public:
  Y2()
    : m_str("What's new, Pussycat?")
  {}

public:
  // Must store return value by value, since the returned value will not persist for the duration of the calling expression
  unused_return_value_monitor<string, string_monitor> fn_by_value()
  {
    return "Hello sailor";
  }

  // Must store return value by (const) reference, since the returned value will persist for the duration of the calling expression
  unused_return_value_monitor<string, string_monitor, string const &> fn_by_ref()
  {
    return m_str;
  }

private:
  string const  m_str;
};


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The documentation for this class was generated from the following file:

• stlsoft_unused_return_value_monitor.h

STLSoft Libraries documentation © Synesis Software Pty Ltd, 2001-2004