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Swift doesn't have a GC and you can use it to program like C with malloc and free via UnsafeMutablePointer<T>. IIRC, Swift's runtime is like C++'s with v-table

Swift doesn't have a GC and you can use it to program like C with malloc and free via UnsafeMutablePointer<T>. IIRC, Swift's runtime is like C++'s with v-table lookup for dispatch on functions that do not involve Objective-C objects.

kibwen 10y ago
Swift's GC is in the form of pervasive reference counting for reference types with no automatic cycle detection. Though as we're demonstrating, calling this GC is contentious, it would be better if people weren't too lazy to type out "pervasive reference counting for reference types with no automatic cycle detection". :P (For the record, I believe Chris Lattner is on the record as saying "yes, Swift has a runtime, let's not bother arguing that point" though I can't find the link, but I agree that Swift's runtime is less invasive than most other languages (e.g. Go).)
- joewillsher 10y ago
  Does saying 'ARC' not work for you? :) And the Swift runtime is pretty minimal, mostly used for storing dynamic type information, dispatching protocol methods, generating (unspecialised) generic types, checking conformances etc. It's mostly used by the compiler to add the dynamic features of the language; for example, the compiler observes the lifetimes of variables and inserts retain/release instructions, which are lowered down to a swift_retain or swift_release calls on the runtime instance. These functions are implemented in the runtime and do the manipulation of reference counts and deallocation.
  - chc 10y ago
    I can see how you'd say that's minimal compared to languages with really huge runtimes — but do you really think it's minimal compared to C or Rust?
  - Someone 10y ago
    It is simpler than a full GC, but I would not call that "pretty minimal". In particular, weak and unowned references and the guarantee that referencing them after the object they referred to was deallocated crashes your program make swift_release nontrivial.
joewillsher 10y ago
Yes, the swift runtime does stuff like heap allocation & reference counting for classes, type introspection (including `as` casts), error handling, as well as generating instances of unspecialised generic types, and dispatching (dynamic) protocol methods (and other witnesses, like computed properties). https://github.com/apple/swift/tree/master/stdlib/public/runtime https://github.com/apple/swift/tree/master/stdlib/public/run...

kibwen 10y ago

Swift's GC is in the form of pervasive reference counting for reference types with no automatic cycle detection. Though as we're demonstrating, calling this GC is contentious, it would be better if people weren't too lazy to type out "pervasive reference counting for reference types with no automatic cycle detection". :P (For the record, I believe Chris Lattner is on the record as saying "yes, Swift has a runtime, let's not bother arguing that point" though I can't find the link, but I agree that Swift's runtime is less invasive than most other languages (e.g. Go).)

joewillsher 10y ago
Does saying 'ARC' not work for you? :) And the Swift runtime is pretty minimal, mostly used for storing dynamic type information, dispatching protocol methods, generating (unspecialised) generic types, checking conformances etc. It's mostly used by the compiler to add the dynamic features of the language; for example, the compiler observes the lifetimes of variables and inserts retain/release instructions, which are lowered down to a swift_retain or swift_release calls on the runtime instance. These functions are implemented in the runtime and do the manipulation of reference counts and deallocation.
- chc 10y ago
  I can see how you'd say that's minimal compared to languages with really huge runtimes — but do you really think it's minimal compared to C or Rust?
- Someone 10y ago
  It is simpler than a full GC, but I would not call that "pretty minimal". In particular, weak and unowned references and the guarantee that referencing them after the object they referred to was deallocated crashes your program make swift_release nontrivial.

joewillsher 10y ago

Yes, the swift runtime does stuff like heap allocation & reference counting for classes, type introspection (including `as` casts), error handling, as well as generating instances of unspecialised generic types, and dispatching (dynamic) protocol methods (and other witnesses, like computed properties). https://github.com/apple/swift/tree/master/stdlib/public/runtime https://github.com/apple/swift/tree/master/stdlib/public/run...