4 ms·

I don't necessarily consider this a fight at all, I think each has their strengths and weaknesses. I much prefer the C++ method, however when programming in Obj

• lloeki 15y ago
  I'd go as far as saying that (Obj)C blocks feel right at home in pure C (where I actually used them more than in ObjC) whereas C++ lambdas fit in, well... C++. I just wish the actual passive-aggressive fight between the FSF and Apple would resolve and blocks could finally make it into upstream GCC C compiler.
  • ben_straub 15y ago
    Not likely. Apple's moved to a clang-based toolchain, haven't they?
    • lloeki 15y ago
      They're still transitioning from pure gcc first to llvm-gcc then to llvm+clang, and blocks are available in all of them. XCode 3.2 defaults to GCC 4.2 with LLVM optionally available and IIRC XCode 4 too (can't check as I downgraded for various reasons). The blocks patchset against pure GCC exists, and the problem mostly lies in upstream GCC refusing patches whose copyright has not been assigned/transferred to the FSF (see https://lwn.net/Articles/405417/ https://lwn.net/Articles/405417/). The rationale is that a critical component such as GCC should not be at the mercy of multiple (possibly hundreds) conflicting parties and easing a possible relicense process to ensure its protection. While I understand the rationale behind this, my opinion is that it feels bureaucratic to the point of hampering notable innovative contributions while favoring local forks which will inevitably end up dying, as maintaining a fork (whatever the patchset size) against the march of a behemoth like GCC is essentially hopeless.
      • Zev 15y ago
        XCode 3.2 defaults to GCC 4.2 with LLVM optionally available and IIRC XCode 4 too (can't check as I downgraded for various reasons). Xcode 4 defaults to llvm-gcc, not gcc-4.2.
        • lloeki 15y ago
          I wasn't quite sure about my memory of it when I wrote it, thanks for the correction. That's still not clang though.
  • calloc 15y ago
    There is no-one at Apple that can sign the copyright for the blocks code over to the FSF and as such it will never happen. At least that was told on the mailing list for LLVM/Clang. I understand why the FSF wants copyright assignment, but it makes the process a lot longer and more complicated.
    • lloeki 15y ago
      Probably Jobs can?
• barrkel 15y ago
  The C++ method doesn't give you a trivial way of capturing variables rather than values, where those variables go on to have a life that matches the lifetime of the closure created. You have to work rather hard to get that, by wrapping things up in little holders which are captured by value, but don't do a deep copy when they themselves are copied. It reminds me a little of how arrays are sometimes used to capture final variables in a mutable way in Java anonymous inner classes. What this means is that whenever you pass off a lambda to a function, and that lambda captures a variable, you need to be aware of whether or not the function keeps a reference to the lambda someplace, so that you'll know if it's safe to capture by reference or not. If you capture by reference but the function keeps a reference to the lambda, and it gets called after the captured variable has gone out of scope, you'll get into some nasty trouble. And this is why I don't like the C++ spec as it stands. It requires a kind of global knowledge to work with correctly in local contexts, in such a way that the compiler can't really help you either (it may have been possible to annotate types to indicate closure lifetime, but it would be painful without more powerful type inference than C++ has).
  • calloc 15y ago
    The issue you mention of not knowing the lifetime is something that happens with pointers and memory allocations as well in C++. Unless it is documented it can be a pain trying to figure out who is ultimately responsible for free'ing the memory that was allocated ... Ultimately Garbage Collection would help there, but I am not sure we are going to see that in C++ anytime soon.
    • barrkel 15y ago
      Yes, but the solution landscape to this problem domain is different. Automatic variables have well-defined lifetimes; they die when they go out of scope. This means there's greater scope for the compiler to take more initiative about lifetime of captured variables (which will all be automatic one way or another, i.e. implicit 'this', a local or a parameter; assume reference parameters etc. cannot be captured). When I designed and implemented the same feature, anonymous methods in Delphi, I used reference counting to keep alive a heap-allocated activation record containing all captured variables. This works well for most scenarios; it can get into knots in more obscure situations where you have recursive lambdas that call themselves via a captured variable, but those are usually pretty rare. You're right that GC is a help. The biggest thing GC gives you is freedom from having to worry about who controls the lifetime of parameters and function return values, in most cases. In the presence of GC, you can get more clever about your algorithms and data structures; you can cache and memoize, without paranoid concern for things disappearing behind your back. Consider a querying API that takes in closures for sorting and selection functions; I can see it building up temporary results and caching them, or streaming results in a multi-threaded fashion, but it can only do that if it can reliably hang on to closures after the select/sort/etc. function has returned.
• bonch 15y ago
  It's not a fight; Mike Ash was just using a tongue-in-cheek headline.