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.