CODEWITHSUNDEEP
c++
Ozymandias
Ozymandias

Reputation: 166

Cascading Function Calls

Using a function that looks like:

IntegerSet &insert(int m);

I'm trying to create a function that supports cascading calls that insert values into an object's array.

My function:

IntegerSet &IntegerSet::insert(int m) {
    IntegerSet newObj;
    for (int i = 0; i < 256; i++) {
        newObj.set1[i] = set1[i]; //copy the array into the new object
    }
    newObj.set1[m] = true;
    return newObj;
}

The object being returned is empty, which I suspect has to do with the reference.

Attempting to change it by altering the & to look like

IntegerSet IntegerSet::&insert(int m)

makes it refuse to compile because it 'expects an identifier'.

Upvotes: 0

Views: 1081

Answers (2)

Joseph Thomson
Joseph Thomson

Reputation: 10433

You should not return a reference to a local, as it will have been destroyed by the time the function returns. However, you probably want to modify the IntegerSet on which you call insert instead and return a reference to *this. This is much more efficient than making a copy each time.

IntegerSet &IntegerSet::insert(int m) {
    set1[m] = true;
    return *this;
}

This way you can chain function calls on an IntegerSet object like so:

iset.insert(1).insert(2).insert(3);

Upvotes: 1

Ben Voigt
Ben Voigt

Reputation: 283793

This is probably what you intended in order to make fluent syntax work:

IntegerSet& IntegerSet::insert(int m)
{
    this->set1[m] = true;
    return *this;
}

For fluent syntax, you typically want a lot of member functions called on the same object, not proliferation of temporary objects.

Upvotes: 3

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