[Development] Qt 5.9's new garbage collector documentation? + root_ptr

[Thiago Macieira]

On sexta-feira, 7 de julho de 2017 18:25:19 PDT Phil Bouchard wrote:
> So if for each function there is 1 root_ptr pointing to a list of local
> variables then:
> - the parameters of the function will remain unaffected if they are used
> as r-values
> - the parameters of the function will require a deep copy of the
> expression if they are used as l-values
> - closures of the function will remain unaffected if they are used as
> r-values
> - closures of the function will require a deep copy of the expression if
> they are used as l-values
> - return values will be deep copies.

JavaScript has no such thing as l or rvalues. Please define use proper terms 
for the language in question.

I don't see a problem with variables being modified. But I do see a problem if 
a parameter is copied to a global variable. Requiring a deep copy is wasteful 
when the current code requires no such thing. So now you have to prove that 
htis extra waste is offset by the benefits of using root_ptr elsewhere.

> function foo(source)
> {
>      var image = new Image();
>      image.height = 100;
>      image.title = file.name;
>      image.src = source; // parameter used as an r-value will remain
> unaffected
>      return image; // return value will require 'image' to be a deep copy
> },

So if this Image object opened a 4K image @ 3840x2160 (= just under 32 MB), 
you're suggesting that all 32 MB be copied?

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center