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Well, like I said in the other comment, you guys could fix that by unbundling the static checker in the Rust compiler and making it applicable to (a subset of)

Well, like I said in the other comment, you guys could fix that by unbundling the static checker in the Rust compiler and making it applicable to (a subset of) C++ code as well :) So then would you agree with the notion that (a practical subset of) C++ combined with a static analyzer could be just as safe and fast as Rust if, hypothetically, there existed an enthusiastic community comparable to Rust's? Or are there intrinsic technical issues? Or syntax issues? Also, let me throw this notion at you: Rather than disallow code that can't be verified to be (memory) safe, the compiler could instead inject runtime checks that would be optimized out using the same analysis that the static checker uses. That is, instead of requiring that the code be fast and safe or it won't compile, it becomes: If your code is not clearly, intrinsically safe then it will have runtime checks that will slow it down. And the compiler could list any runtime checks that it wasn't able to optimize out. The reason I suggest this is that memory safety is just the enforcement of certain invariants. There's no reason why we couldn't let the programmer define additional, application specific invariants and have the build process treat them the same way it treats memory access invariants. So for example, when a user defines a class, it could have a standard member function called "assert_object_invariants()" or something, that the programmer can define. Then anytime a (non-const?) member function is called, the compiler can insert runtime asserts at the beginning and end of the member function call. And again the compiler can tell you when those runtime asserts aren't optimized out. Wouldn't that make sense? I haven't really thought it through.

Manishearth 10y ago
> Well, like I said in the other comment, you guys could fix that by unbundling the static checker in the Rust compiler and making it applicable to (a subset of) C++ code as well :) The problem is that you still need extra annotations. Namely lifetime annotations (or something similar relating between borrows -- either that, or use a lot of elision which can be crippling). On top of that, the programming style Rust encourages is not the same as the ones you tend to see in C++ codebase, and programming in the C++ style will lead to code that doesn't compile. > Rather than disallow code that can't be verified to be (memory) safe, the compiler could instead inject runtime checks that would be optimized out using the same analysis that the static checker uses. This might be more tractable (and is an interesting idea). But that optimizer would be hard to write. > So then would you agree with the notion that (a practical subset of) C++ combined with a static analyzer could be just as safe and fast as Rust I think this is what the new ISOCPP core guidelines are trying to do? Though they don't go far enough in preventing memory unsafety IIRC (this may have changed).
- duneroadrunner 10y ago
  > The problem is that you still need extra annotations. Namely lifetime annotations Well, the idea is not to have the static analyzer verify typical C++ code. Just some practical subset. So for example I think it's quite practical to write C++ code that uses only "scope" pointers (basically pointers to objects on the stack) and (not-null) refcounting pointers, that intrinsically don't outlive their targets. Lifetimes would be implied by the types. So wait, what more does Rust's static analyzer give us again? Does it somehow remove the need for refcounting heap objects? > the programming style Rust encourages is not the same as the ones you tend to see in C++ codebase, and programming in the C++ style will lead to code that doesn't compile. I have no problem with that. I have no attachment to the "traditional" C++ programming style. > This might be more tractable (and is an interesting idea). But that optimizer would be hard to write. Why? The static analyzer has an opinion on whether or not a program is safe. The optimizer just wants to know if it still thinks it's safe when you remove a runtime check. > I think this is what the new ISOCPP core guidelines are trying to do? Though they don't go far enough in preventing memory unsafety IIRC (this may have changed). The ISOCPP core guidelines approach is to recommend the use of C++'s intrinsically dangerous elements in a way that is "usually safe", but not always, and rely on their static analyzer to catch bugs. So the question becomes, what do you do in the many cases where the static analyzer doesn't know if it's safe or not. You can try to redesign your code so the static analyzer can understand that it's safe. But that's often very inconvenient or has a performance cost. Often the most practical (safe) solution is to resort to something like SaferCPlusPlus.
  - Manishearth 10y ago
    > So wait, what more does Rust's static analyzer give us again? Does it somehow remove the need for refcounting heap objects? Refcounting is rarely needed because most sharing is done via "borrows", which usually work via scope-tied "references" which may point to either the stack or the heap. Implementing and enforcing local scope pointers in C++ via static analysis is not hard. Making it possible to thread borrows through APIs and annotate things with the borrowing semantics (which is what makes Rust avoid refcounting or even allocation costs) requires a bit more work. > I have no attachment to the "traditional" C++ programming style. Right, but at this point you have a very weird looking subset of C++ that can't seamlessly integrate with other libraries, and can't be translated to from regular C++ without significant human intervention -- why not just use Rust? > Why? The static analyzer has an opinion on whether or not a program is safe. The optimizer just wants to know if it still thinks it's safe when you remove a runtime check. I guess I misunderstood your proposal. This sounds doable. But, again, you'd be using a weird subset of C++ that doesn't seamlessly integrate, and you're just better off using Rust at this point. Instead of trying to port Rust's guarantees to C++ it makes more sense to use the same principles to organically build on top of C++, in a different way. IMO this is sort of what ISOCPP is trying to do, but they're not quite there yet, and trying to find a compromise between making the language too different and making it safe is hard. > So the question becomes, what do you do in the many cases where the static analyzer doesn't know if it's safe or not. You can try to redesign your code so the static analyzer can understand that it's safe. This is always going to be a problem regardless of the static analyzer. You have to design it to reject these cases. Rust does this too; there are some edge cases where you need to design around the borrow checker (though usually this doesn't incur additional cost, and the most common of these are going to be addressed). If designing low level abstractions like vectors and stuff (or doing FFI), Rust gives you an escape hatch ("unsafe"), which has a couple of checks disabled and can be used to write the code you need (verifying safety of a program then just requires verifying that these blocks of code are sound and do not rely on any invariants that can be broken by code outside of them).
pcwalton 10y ago
> Well, like I said in the other comment, you guys could fix that by unbundling the static checker in the Rust compiler and making it applicable to (a subset of) C++ code as well :) No, we can't do that. It is incompatible with C++. > Rather than disallow code that can't be verified to be (memory) safe, the compiler could instead inject runtime checks that would be optimized out using the same analysis that the static checker uses. That is not possible. It would require massive bookkeeping, much like your library does. That would eliminate most of the benefits of Rust.

Manishearth 10y ago

> Well, like I said in the other comment, you guys could fix that by unbundling the static checker in the Rust compiler and making it applicable to (a subset of) C++ code as well :) The problem is that you still need extra annotations. Namely lifetime annotations (or something similar relating between borrows -- either that, or use a lot of elision which can be crippling). On top of that, the programming style Rust encourages is not the same as the ones you tend to see in C++ codebase, and programming in the C++ style will lead to code that doesn't compile. > Rather than disallow code that can't be verified to be (memory) safe, the compiler could instead inject runtime checks that would be optimized out using the same analysis that the static checker uses. This might be more tractable (and is an interesting idea). But that optimizer would be hard to write. > So then would you agree with the notion that (a practical subset of) C++ combined with a static analyzer could be just as safe and fast as Rust I think this is what the new ISOCPP core guidelines are trying to do? Though they don't go far enough in preventing memory unsafety IIRC (this may have changed).

duneroadrunner 10y ago
> The problem is that you still need extra annotations. Namely lifetime annotations Well, the idea is not to have the static analyzer verify typical C++ code. Just some practical subset. So for example I think it's quite practical to write C++ code that uses only "scope" pointers (basically pointers to objects on the stack) and (not-null) refcounting pointers, that intrinsically don't outlive their targets. Lifetimes would be implied by the types. So wait, what more does Rust's static analyzer give us again? Does it somehow remove the need for refcounting heap objects? > the programming style Rust encourages is not the same as the ones you tend to see in C++ codebase, and programming in the C++ style will lead to code that doesn't compile. I have no problem with that. I have no attachment to the "traditional" C++ programming style. > This might be more tractable (and is an interesting idea). But that optimizer would be hard to write. Why? The static analyzer has an opinion on whether or not a program is safe. The optimizer just wants to know if it still thinks it's safe when you remove a runtime check. > I think this is what the new ISOCPP core guidelines are trying to do? Though they don't go far enough in preventing memory unsafety IIRC (this may have changed). The ISOCPP core guidelines approach is to recommend the use of C++'s intrinsically dangerous elements in a way that is "usually safe", but not always, and rely on their static analyzer to catch bugs. So the question becomes, what do you do in the many cases where the static analyzer doesn't know if it's safe or not. You can try to redesign your code so the static analyzer can understand that it's safe. But that's often very inconvenient or has a performance cost. Often the most practical (safe) solution is to resort to something like SaferCPlusPlus.
- Manishearth 10y ago
  > So wait, what more does Rust's static analyzer give us again? Does it somehow remove the need for refcounting heap objects? Refcounting is rarely needed because most sharing is done via "borrows", which usually work via scope-tied "references" which may point to either the stack or the heap. Implementing and enforcing local scope pointers in C++ via static analysis is not hard. Making it possible to thread borrows through APIs and annotate things with the borrowing semantics (which is what makes Rust avoid refcounting or even allocation costs) requires a bit more work. > I have no attachment to the "traditional" C++ programming style. Right, but at this point you have a very weird looking subset of C++ that can't seamlessly integrate with other libraries, and can't be translated to from regular C++ without significant human intervention -- why not just use Rust? > Why? The static analyzer has an opinion on whether or not a program is safe. The optimizer just wants to know if it still thinks it's safe when you remove a runtime check. I guess I misunderstood your proposal. This sounds doable. But, again, you'd be using a weird subset of C++ that doesn't seamlessly integrate, and you're just better off using Rust at this point. Instead of trying to port Rust's guarantees to C++ it makes more sense to use the same principles to organically build on top of C++, in a different way. IMO this is sort of what ISOCPP is trying to do, but they're not quite there yet, and trying to find a compromise between making the language too different and making it safe is hard. > So the question becomes, what do you do in the many cases where the static analyzer doesn't know if it's safe or not. You can try to redesign your code so the static analyzer can understand that it's safe. This is always going to be a problem regardless of the static analyzer. You have to design it to reject these cases. Rust does this too; there are some edge cases where you need to design around the borrow checker (though usually this doesn't incur additional cost, and the most common of these are going to be addressed). If designing low level abstractions like vectors and stuff (or doing FFI), Rust gives you an escape hatch ("unsafe"), which has a couple of checks disabled and can be used to write the code you need (verifying safety of a program then just requires verifying that these blocks of code are sound and do not rely on any invariants that can be broken by code outside of them).

pcwalton 10y ago

> Well, like I said in the other comment, you guys could fix that by unbundling the static checker in the Rust compiler and making it applicable to (a subset of) C++ code as well :) No, we can't do that. It is incompatible with C++. > Rather than disallow code that can't be verified to be (memory) safe, the compiler could instead inject runtime checks that would be optimized out using the same analysis that the static checker uses. That is not possible. It would require massive bookkeeping, much like your library does. That would eliminate most of the benefits of Rust.