3 ms·

I don't understand. Smart pointers replace dumb pointers not normal stack/inline object placement.

flohofwoe 4y ago
Yes, but people need to be aware that "auto obj = make_unique..." or "auto obj = make_shared..." should be a very rare thing and not the norm (and I've seen plenty code bases like that). There needs to be a proper memory management strategy with the goal of minimizing heap allocation in random places in the code. E.g. automatic memory management doesn't resolve you from thinking just as much about memory management than doing it manually in the first place.
- gpderetta 4y ago
  I would hope they are, otherwise why are you even writing C++. I might have too high expectations though...
  - flohofwoe 4y ago
    The idea that ref-counting is automatically "better" than a garbage collector is still pretty popular unfortunately (and that's just the tip of the iceberg).
    - nu11ptr 4y ago
      A bump allocator + state of the art compacting GC is MUCH faster on a naïve basis which is why it is important to minimize number of allocations in non-GC langs and use stack based RAII when possible. When building things like trees in a non-GC language, arena allocation should be considered for max performance. This is just another low level vs high level trade off IMO.
      - pkolaczk 4y ago
        > A bump allocator + state of the art compacting GC is MUCH faster I can see it repeated very often, but can you point me to any evidence for such claim, based on modern low-pause GCs and real data (not simulation)? I find low pause GCs have pretty substantial overhead and have way lower allocation throughput than old stop-the-world GCs. And the difference between manual memory allocation wasn't that big either (still within 2x).
jstimpfle 4y ago
It's not about what you use to point to the thing. It's about how you allocate the thing in the first place. Smart pointers are like a free pass to do things without consideration: they allow you to make progress without caring how your things are allocated, because they ease the pain that results from just allocating stuff on the global heap, lacking a systematic approach. Note that while smart pointers ease pain in the short term, there are subtle complications that arise from the constraints that they introduce. One is performance, in some cases the cost of generalized memory management can be too much. Memory fragmentation can be an issue too. RAII the mechanism is not free but requires compatible code and containers. I'm sure there are lots of projects that have broken under the added constraints introduce by such smart classes. And while smart pointers are orthogonal to systematic memory management, if you get the management right the use of smart pointers can easily become a net negative.
- gpderetta 4y ago
  I don't subscribe to the 'it is expensive so it should be painful' line of thought. That's how you end up with cstrings, strcpy, strdup and friends.
  - jstimpfle 4y ago
    No, strdup uses a general purpose allocator to put a string in a random place on the heap. Quite the opposite of a well-structured approach. "It is complicated so let's see if there is a simpler approach".

Yes, but people need to be aware that "auto obj = make_unique..." or "auto obj = make_shared..." should be a very rare thing and not the norm (and I've seen plenty code bases like that). There needs to be a proper memory management strategy with the goal of minimizing heap allocation in random places in the code. E.g. automatic memory management doesn't resolve you from thinking just as much about memory management than doing it manually in the first place.

gpderetta 4y ago
I would hope they are, otherwise why are you even writing C++. I might have too high expectations though...
- flohofwoe 4y ago
  The idea that ref-counting is automatically "better" than a garbage collector is still pretty popular unfortunately (and that's just the tip of the iceberg).
  - nu11ptr 4y ago
    A bump allocator + state of the art compacting GC is MUCH faster on a naïve basis which is why it is important to minimize number of allocations in non-GC langs and use stack based RAII when possible. When building things like trees in a non-GC language, arena allocation should be considered for max performance. This is just another low level vs high level trade off IMO.
    - pkolaczk 4y ago
      > A bump allocator + state of the art compacting GC is MUCH faster I can see it repeated very often, but can you point me to any evidence for such claim, based on modern low-pause GCs and real data (not simulation)? I find low pause GCs have pretty substantial overhead and have way lower allocation throughput than old stop-the-world GCs. And the difference between manual memory allocation wasn't that big either (still within 2x).

jstimpfle 4y ago

It's not about what you use to point to the thing. It's about how you allocate the thing in the first place. Smart pointers are like a free pass to do things without consideration: they allow you to make progress without caring how your things are allocated, because they ease the pain that results from just allocating stuff on the global heap, lacking a systematic approach. Note that while smart pointers ease pain in the short term, there are subtle complications that arise from the constraints that they introduce. One is performance, in some cases the cost of generalized memory management can be too much. Memory fragmentation can be an issue too. RAII the mechanism is not free but requires compatible code and containers. I'm sure there are lots of projects that have broken under the added constraints introduce by such smart classes. And while smart pointers are orthogonal to systematic memory management, if you get the management right the use of smart pointers can easily become a net negative.

gpderetta 4y ago
I don't subscribe to the 'it is expensive so it should be painful' line of thought. That's how you end up with cstrings, strcpy, strdup and friends.
- jstimpfle 4y ago
  No, strdup uses a general purpose allocator to put a string in a random place on the heap. Quite the opposite of a well-structured approach. "It is complicated so let's see if there is a simpler approach".