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x = f();

2 replies on 1 page. Most recent reply: Aug 5, 2005 10:25 PM by Christopher Diggins

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Christopher Diggins

Posts: 1215
Nickname: cdiggins
Registered: Feb, 2004

x = f(); (View in Weblogs)

Posted: Aug 5, 2005 4:48 PM

Summary
This is a very simple statement, but I don't like what C++ does with it.

In C++ the following code creates an extra temporary:

class MyClass {
  ...
  int m[1000000]
}

MyClass f() {
  MyClass ret;
  ...
  return ret;
}

int main() {
  MyClass x = f();
}

In Heron I am seriously considering rewriting code like that to behave like:

class MyClass {
  ...
  int m[1000000]
}

void f(MyClass& ret) {
  ...
}

int main() {
  MyClass x;
  f(x);
}

This avoids the creation of a superflous temporary. Could programmers live with the difference?

Tanton Gibbs

Posts: 20
Nickname: tanton
Registered: Aug, 2005

Re: x = f();

Posted: Aug 5, 2005 6:30 PM

It is my understanding that C++ already works like that. The Named Return Value Optimization should cause C++ to work exactly like your Heron code.

http://www.devx.com/tips/Tip/5716

Christopher Diggins

Posts: 1215
Nickname: cdiggins
Registered: Feb, 2004

Re: x = f();

Posted: Aug 5, 2005 10:25 PM

> It is my understanding that C++ already works like that.
> The Named Return Value Optimization should cause C++ to
> o work exactly like your Heron code.
>
> http://www.devx.com/tips/Tip/5716

As Mr. Burns of the Simpsons likes to say "Excellent".

Thanks for pointing that out, this makes my life much easier.

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