Are there any valid use cases to use new and delete, raw pointers or c-style arrays with modern C++?

Question

Here's a notable video (Stop teaching C) about that paradigm change to take in teaching the c++ language.

And an also notable blog post

I have a dream ...

I'm dreaming of so called C++ courses/classes/curriculae will stop teaching (requiring) their students to use: ...

Since C++11 as established standard we have the Dynamic memory management facilities aka smart pointers.
Even from earlier standards we have the c++ standard Containers library as a good replacement for raw arrays (allocated with new T[]) (notably usage of std::string instead of c-style NUL terminated character arrays).

Question(s) in bold:

Let aside the placement new override, is there any valid use case that can't be achieved using smart pointers or standard containers but only using new and delete directly (besides implementation of such container/smart pointer classes of course)?

It's sometimes rumored (like here or here) that using new and delete handrolled can be "more efficient" for certain cases. Which are these actually? Don't these edge cases need to keep track of the allocations the same way as standard containers or smart pointers need to do?

Almost the same for raw c-style fixed size arrays: There is std::array nowadays, which allows all kinds of assignment, copying, referencing, etc. easily and syntactically consistent as expected by everyone. Are there any use cases to choose a T myArray[N]; c-style array in preference of std::array<T,N> myArray;?

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Regarding interaction with 3rd party libraries:

Assumed a 3rd party library returns raw pointers allocated with new like

MyType* LibApi::CreateNewType() {     return new MyType(someParams); } 

you can always wrap that to a smart pointer to ensure that delete is called:

std::unique_ptr<MyType> foo = LibApi::CreateNewType(); 

even if the API requires you to call their legacy function to free the resource like

void LibApi::FreeMyType(MyType* foo); 

you still can provide a deleter function:

std::unique_ptr<MyType, LibApi::FreeMyType> foo = LibApi::CreateNewType(); 

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I'm especially interested in valid "every day" use cases in contrast to academic/educational purpose requirements and restrictions, which aren't covered by the mentioned standard facilities.
That new and delete may be used in memory management / garbage collector frameworks or standard container implementation is out of question¹.

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One major motivation ...

... to ask this question is to give an alternative approach vs any (homework) questions, which are restricted to use any of the constructs mentioned in the title, but serious questions about production ready code.

These are often referred to as the basics of memory management, which is IMO blatantly wrong/misunderstood as suitable for beginners lectures and tasks.

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¹⁾_{Add.: Regarding that paragraph, this should be a clear indicator that new and delete isn't for beginner c++ students, but should be left for the more advanced courses.}

Answer 1

When ownership should not be local.

As an example, a pointer container may not want ownership over the pointers in it to reside in the pointers themselves. If you try to write a linked list with forward unique ptrs, at destruction time you can easily blow the stack.

A vector-like container of owning pointers may be better suited to storing delete operation at the container or subcontainer level, and not at the element level.

In those and similar cases, you wrap ownership like a smart pointer does, but you do it at a higher level. Many data structures (graphs, etc) may have similar issues, where ownership properly resides at a higher point than where the pointers are, and they may not map directly to an existing container concept.

In some cases it may be easy to factor out the container-ownership from the rest of the data structure. In others it may not.

Sometimes you have insanely complex non-local non-reference counted lifetimes. There is no sane spot to put the ownership pointer in those cases.

Determining correctness here is hard, but not impossible. Programs that are correct and have such complex ownership semantics exist.

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All of these are corner cases, and few programmers should run into them more than a handful of times in a career.

Answer 2

I'm going to be contrarian, and go on record as saying "no" (at least to the question I'm pretty sure you really intended to ask, for most of the cases that have been cited).

What seem like obvious use-cases for using new and delete (e.g., raw memory for a GC heap, storage for a container) really aren't. For these cases, you want "raw" storage, not an object (or array of objects, which is what new and new[] provide respectively).

Since you want raw storage, you really need/want to use operator new and operator delete to manage the raw storage itself. You then use placement new to create objects in that raw storage, and directly invoke the destructor to destroy the objects. Depending on the situation, you might want to use a level of indirection to that though--for example, the containers in the standard library use an Allocator class to handle these tasks. This is passed as a template parameter, which provides a customization point (e.g., a way to optimize allocation based on a particular container's typical usage pattern).

So, for these situations, you end up using the new keyword (in both the placement new and the invocation of operator new), but not something like T *t = new T[N];, which is what I'm pretty sure you intended to ask about.