C++Guns – RoboBlog blogging the bot

29.07.2015

DerivedFunctor - fancy

Filed under: Allgemein — Tags: — Thomas @ 22:07

In C++11 kann man von einer Funktion erben. Krass.
Lambdas sind krass.
Das typedef musste sein, sonst hat er nicht compiliert. Ist vllt aber
nur ein Compilerbug und bald nicht mehr nötig.

auto foo = [](){return 42;};

class DerivedFunctor : public decltype(foo)
{
  typedef decltype(foo) type;
  public:
    DerivedFunctor(type foo)
    : type(foo)
    {
    }

    auto operator()() {
      cout << "DerivedFunctor::operator()\n";
      return type::operator()();
    }
};

int main() {
  DerivedFunctor t(foo);
  cout << t();
}

26.07.2015

Replace runtime constant wich template variables

Filed under: Allgemein — Tags: — Thomas @ 09:07 

void version1(int i, int h) {
  // if(h) is evaluated every call
  if(h==0) {
  }
  else if(h==1) {
  }
  else {
  }
}

template
void version2(int i) {
  // if(h) is evaluated at compile time
  if(h==0) {
  }
  else if(h==1) {
  }
  else {
  }
}

void func(int h) {
  // h is a runtime constant for this function
  for(int i=0; i < 1e7; ++i) {
    version1(i, h);
  }

  // here,h is evaluated at runtime but outside the loop.
  // the compiler create three different version of version2 each for every h
  if(h==0) {
    for(int i=0; i < 1e7; ++i) {
      version2<0>(i);
    }
  }
  else if(h==1) {
    for(int i=0; i < 1e7; ++i) {
      version2<1>(i);
    }
  }
  else {
    for(int i=0; i < 1e7; ++i) {
      version2<2>(i);
    }
  }
}

int main() {
  int h=0;
  func(h);

  h=1;
  func(h);
}

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