67 ms·

That isn't quite true. Swift will be using LLVM as a code generator, but because it will use ARC (a form of garbage collection), it will still end up slower th

That isn't quite true. Swift will be using LLVM as a code generator, but because it will use ARC (a form of garbage collection), it will still end up slower than C++ in many benchmarks. That's not the only example, of course--while LLVM helps immensely, it's not a miracle worker and the original language semantics do make a difference.

pjmlp 12y ago
This is not true, as Swift ARC is supported by the compiler itself, whereas C++ ARC are library based without any compiler supporter. So a Swift compiler will be able to optimize away ARC calls deemed unnecessary via dataflow optimizations, which a C++ cannot apply.
- dbaupp 12y ago
  I think C++ give you many more tools to avoid using "ARCs", e.g other smart pointers, not needing smart pointers at all etc.
  - pjmlp 12y ago
    Not using smart pointers is "memory leaks and security exploits" land. RAII is great, but not when dealing with shared data structures. So I lack to see how it can be better. Note that I am a big C++ fan since the C++ARM days, but I am also aware of many of its warts.
    - dbaupp 12y ago
      I just meant you don't need necessarily need pointers at all, since you put things directly onto the stack (or into vectors/your favourite data structure), no need for additional indirection. (Maybe Swift offers this too, but it's certainly something C++ excels at.)
      - pjmlp 12y ago
        Funny to see stack allocation mentioned as C++ strong feature, when so many languages offer it. Maybe this is a side effect of scripting languages and VM implementations going mainstream.
        dbaupp 12y ago
        Please, be direct with your criticisms of me rather than just implying them. What other commonly used languages offer pointerlessness to the same degree as C++? Rust, for sure. Not C as there are no generics, making allocations + void* and simplistic data structures like linked lists more common than necessary. Maybe D but AIUI there is some struct/class difference that forces GC allocation for classes. What else? (Also, please read my original comment properly, I was not just talking about "stack allocation".)
        pjmlp 12y ago
        I am just answering about placing data into the stack, and that is offered by all descendents of Algol/Pascal/CLU/Mesa/Modula/Ada/... family of languages. You can place data in the stack in all of them. Quite a few of them allow for generics, starting with CLU. Ada also offers RAII, although a bit more verbose than C++ way of doing it. All of them allow reference arguments, hence no need for pointers for output parameters.
        dbaupp 12y ago
        RAII is totally irrelevant to this discussion, and I clearly said I was not just talking about placing data on the stack. > All of them allow reference arguments, hence no need for pointers for output parameters. I wasn't very clear, the use of a C-style pointer is irrelevant: if it is being used as a reference (i.e. not owning, no need for clean-up/deallocation), then it counts as a reference. I was using the Rust terminology where 'pointer' mostly refers to 'smart pointer'.
      - deleted 12y ago
        [deleted]
rsynnott 12y ago
> but because it will use ARC (a form of garbage collection), it will still end up slower than C++ in many benchmarks Well, depends on the C++. ARC is reference counting behind the scenes; in Objective C and Swift, the compiler inserts retains and releases as appropriate. A lot of C++ code also uses reference counting a fair bit; that's what shared_ptr is for, for instance.

pjmlp 12y ago

This is not true, as Swift ARC is supported by the compiler itself, whereas C++ ARC are library based without any compiler supporter. So a Swift compiler will be able to optimize away ARC calls deemed unnecessary via dataflow optimizations, which a C++ cannot apply.

dbaupp 12y ago
I think C++ give you many more tools to avoid using "ARCs", e.g other smart pointers, not needing smart pointers at all etc.
- pjmlp 12y ago
  Not using smart pointers is "memory leaks and security exploits" land. RAII is great, but not when dealing with shared data structures. So I lack to see how it can be better. Note that I am a big C++ fan since the C++ARM days, but I am also aware of many of its warts.
  - dbaupp 12y ago
    I just meant you don't need necessarily need pointers at all, since you put things directly onto the stack (or into vectors/your favourite data structure), no need for additional indirection. (Maybe Swift offers this too, but it's certainly something C++ excels at.)
    - pjmlp 12y ago
      Funny to see stack allocation mentioned as C++ strong feature, when so many languages offer it. Maybe this is a side effect of scripting languages and VM implementations going mainstream.
      - dbaupp 12y ago
        Please, be direct with your criticisms of me rather than just implying them. What other commonly used languages offer pointerlessness to the same degree as C++? Rust, for sure. Not C as there are no generics, making allocations + void* and simplistic data structures like linked lists more common than necessary. Maybe D but AIUI there is some struct/class difference that forces GC allocation for classes. What else? (Also, please read my original comment properly, I was not just talking about "stack allocation".)
        pjmlp 12y ago
        I am just answering about placing data into the stack, and that is offered by all descendents of Algol/Pascal/CLU/Mesa/Modula/Ada/... family of languages. You can place data in the stack in all of them. Quite a few of them allow for generics, starting with CLU. Ada also offers RAII, although a bit more verbose than C++ way of doing it. All of them allow reference arguments, hence no need for pointers for output parameters.
        dbaupp 12y ago
        RAII is totally irrelevant to this discussion, and I clearly said I was not just talking about placing data on the stack. > All of them allow reference arguments, hence no need for pointers for output parameters. I wasn't very clear, the use of a C-style pointer is irrelevant: if it is being used as a reference (i.e. not owning, no need for clean-up/deallocation), then it counts as a reference. I was using the Rust terminology where 'pointer' mostly refers to 'smart pointer'.
    - deleted 12y ago
      [deleted]

rsynnott 12y ago

> but because it will use ARC (a form of garbage collection), it will still end up slower than C++ in many benchmarks Well, depends on the C++. ARC is reference counting behind the scenes; in Objective C and Swift, the compiler inserts retains and releases as appropriate. A lot of C++ code also uses reference counting a fair bit; that's what shared_ptr is for, for instance.