I wish that container.contains() would return the actual value...

[Dariusz]

Hey...

Am I the only one who finds doing this :

if(map.cotnains(key)){
    auto *item = map[key];
   map.remove(key);
   delete item;
}

Could have been handled by

if(auto *item = map.contains(key)){
    map.remove(key);
    delete item;
    }

And so on and so forth?
1 Less function call but on a large scale, it might help?

[jsulm]

@dariusz It would be counter-intuitive, because "contains" does what it means: it tells you whether container contains something. A simple yes/no answer. Also, what should it return if there is no such element?
Last but not least there is https://doc.qt.io/qt-5/qvector.html#value or https://doc.qt.io/qt-5/qmap.html#value which does what you want...

[Dariusz]

@jsulm said in I wish that container.contains() would return the actual value...:

@dariusz It would be counter-intuitive, because "contains" does what it means: it tells you whether container contains something. A simple yes/no answer. Also, what should it return if there is no such element?

I was thinking of it lately, I suppose containsPtr(), would return either nullptr=false or item = true ?

Last but not least there is https://doc.qt.io/qt-5/qvector.html#value or https://doc.qt.io/qt-5/qmap.html#value which does what you want...

Heee I never thought of using value()! So if its map of Ptrs, would default value return be a nullptr? As if he just make new item from default constructor then thats no help, I will have to test if the item is "valid" and then delete if its not mhmmm

[SGaist]

Hi,

The function takes two parameters. You can pass the default value you want to get if the key is not found in the map.

[JKSH]

@dariusz said in I wish that container.contains() would return the actual value...:

if(map.cotnains(key)){
    auto *item = map[key];
   map.remove(key);
   delete item;
}

This whole block can be replaced by 1 line:

delete map.take(key);

take() returns the item and removes it from the map. If the map does not contain key, take() returns a default value (nullptr, in your case). It is safe to delete nullptr as long as you don't use a non-standard deallocator.

[Dariusz]

Thats actually pretty awesome... for deleting! Neat thank you!

What about this scenario?

    if (map.contains(key)) {
        map[key] = "do Stuff";
    } else {
        qDebug() << "invalid key ? ";
    }

Any better way of solving this double search ?

TIA!

[Chris Kawa]

Any better way of solving this double search ?

Yes, the classic stl style:

auto it = map.find(key);
if (it != map.end()) {
   *it = "do Stuff";
}
else {
   qDebug() << "invalid key ? ";
}

If you don't like that it's one line longer you can use c++17:

if (auto it = map.find(key); it != map.end()) {

[Dariusz]

Amazing thank you! :- D

I'm a tad handicapped with Qt being so nice and me not knowing 60% of STL...

Now just gotta rewrite few...hundreds...of lines of code :D

[Chris Kawa]

@dariusz said

me not knowing 60% of STL

I would concentrate on fixing that. You're missing a large chunk of ready to use stuff and you'll be reinventing a lot of wheels without it.