Function chaining and data loss

Question

When I started with c++ initially, we were taught that function chaining work only with return value by reference. Otherwise data loss occurs if we use return by value.

If I remember correctly, it was for assigning three objects in a single line for assignment operator overloading.

Is above still correct?

I heard today that builder pattern can return builder object by value and it should not be a problem of data loss. Performance may hit but data loss is not the concern.

Answer 1

can you post a sample code?

can you elaborate a bit more about the data loss part?

the simplest method chaining implementation I can think at the moment looks something like this:

https://sololearn.com/compiler-playground/ck8m0D7ZcEGJ/?ref=app

but i would avoid using this pattern because it's harder to debug when something goes wrong.

Answer 2

Bob_Li thanks for putting this sample code.

Why you had returned Car& from all the method ? You could have returned simple car from each method .

Is it not necessary to return Car&

Answer 3

Bob_Li here is the trial finally. I could still reproduce this it seems.

Means inconsistent behaviour apart from copy constructor cost.

Refer code below:

https://sololearn.com/compiler-playground/cOYfNI37BKT0/?ref=app

It results into data loss. If I had all the methods returning &, we could have proper results.