5 ms·

But how do you go beyond the paradigm of linear / affine types and nested regions that Rust gives you when you remove GC? Lots of programs are difficult to writ

But how do you go beyond the paradigm of linear / affine types and nested regions that Rust gives you when you remove GC? Lots of programs are difficult to write with only these features, e.g. a web browser, and when you do you just end up writing a garbage collector yourself anyways. Either you add optional unrestricted allocations or increase the complexity of the type system to allow for the expression of more safe deallocation using dependent types or another similarly strong logic. I really like Rust, but I wonder how it is going to get over this hurdle that previous languages like Cyclone never fully solved.

kibwen 13y ago
The title of this post is somewhat misleading. Just because pcwalton wants to remove GC from the language doesn't mean that GC won't be available, just that it would be transformed from a compiler mechanism into a module in the standard library. The semantics would be exactly the same, though the syntax to use it would change a bit. The goal here isn't to hate on GC, it's to ensure that normal users are capable of implementing pointer types that are exactly as "blessed" as the built-in types--and the best way to do that is by eating your own dogfood.
- cwzwarich 13y ago
  pcwalton both wrote the article and the comment I was replying to. If GC isn't necessary because Rust's type system can prove that the deallocations are safe then the answer to the question of how to write programs with nontrivial memory allocation patterns shouldn't be "use an external unsafe GC".
  - kibwen 13y ago
    The existence of Rust's current GC doesn't have anything to do with preventing dangling pointers. Off the top of my head, cyclical references are the only thing that you need GC for that you can't handle with unique pointers or borrowed pointers, but there may be others. I would need to have read Andrei's original argument to be sure, but I'm guessing it was along the lines of "without a strong type system, garbage collection is necessary to prevent dangling pointers". And Rust's type system is strong enough to prevent dangling pointers; they cannot happen unless you are deliberately dropping into `unsafe` blocks. This is true regardless of if you have garbage collection built in. But that doesn't necessarily mean that the type system is powerful enough to encode all the patterns that GC allows.

kibwen 13y ago

The title of this post is somewhat misleading. Just because pcwalton wants to remove GC from the language doesn't mean that GC won't be available, just that it would be transformed from a compiler mechanism into a module in the standard library. The semantics would be exactly the same, though the syntax to use it would change a bit. The goal here isn't to hate on GC, it's to ensure that normal users are capable of implementing pointer types that are exactly as "blessed" as the built-in types--and the best way to do that is by eating your own dogfood.

cwzwarich 13y ago
pcwalton both wrote the article and the comment I was replying to. If GC isn't necessary because Rust's type system can prove that the deallocations are safe then the answer to the question of how to write programs with nontrivial memory allocation patterns shouldn't be "use an external unsafe GC".
- kibwen 13y ago
  The existence of Rust's current GC doesn't have anything to do with preventing dangling pointers. Off the top of my head, cyclical references are the only thing that you need GC for that you can't handle with unique pointers or borrowed pointers, but there may be others. I would need to have read Andrei's original argument to be sure, but I'm guessing it was along the lines of "without a strong type system, garbage collection is necessary to prevent dangling pointers". And Rust's type system is strong enough to prevent dangling pointers; they cannot happen unless you are deliberately dropping into `unsafe` blocks. This is true regardless of if you have garbage collection built in. But that doesn't necessarily mean that the type system is powerful enough to encode all the patterns that GC allows.