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Beyond just performance, RAII (a cryptically named concept BTW) introduces a lot of implicit, indirect behavior, making code much more complicated and harder to

Beyond just performance, RAII (a cryptically named concept BTW) introduces a lot of implicit, indirect behavior, making code much more complicated and harder to reason about. When does your constructor & destructor fire when a dynamic array grows? Did you use the copy-and-swap idiom properly? Did you define all the "rule of five" methods? It's bonkers. I think a "defer" or "on scope exit" statement is just about ideal, gets you the same benefits but much more simply.

Measter 2y ago
> When does your constructor & destructor fire when a dynamic array grows? What constructor? And why would a Drop implementation be invoked to move something? You've moved it, there's nothing left to drop. > Did you use the copy-and-swap idiom properly? I don't believe I'm familiar with this idiom? From some quick googling this seems to be related to panic safety and ensuring that you don't leave things in an invalid state if a panic happens. It doesn't seem to be RAII-specific, and would also apply to a defer mechanism. > Did you define all the "rule of five" methods? Rule of five? You mean that your Clone implementation must properly handle resources in accordance with your Drop implementation, right? I'm not sure where the other three come in?
- QuadrupleA 2y ago
  I'm speaking about C++, where blind faith in RAII is widespread, so I don't know if Rust's implementation alleviates some of the accidental complexity. But I suspect any system with constructors / destructors leads to a lot of the same implicit behaviors, unintended complications, and leaky abstractions, and I generally favor explicit Initialize() and Cleanup() functions that you call manually, even in languages that support the implicit/magic stuff.
  - estebank 2y ago
    Rust doesn't have constructors*. * Well, it kind of does, in so far there is a Ctor enum variant in the compiler implementation to represent the name of a type in the value namespace, but it is not overridable by end users and has no logic.
  - Measter 2y ago
    You were conflating details of C++'s object model and implementation of move semantics with RAII. Rust also makes heavy use of RAII, and the details of its object model and move semantics are not the same as C++'s. The only thing that RAII requires is the concept of ownership, and a cleanup function that the compiler knows about. The one implicit thing here is the automatic insertion of calls to the cleanup function.
csb6 2y ago
Rust does not have the rule of five, and it does not really have copy/move constructors. defer does not get you the same benefits as a destructor because you can easily forget to write a defer, while destructors are always called.

Measter 2y ago

> When does your constructor & destructor fire when a dynamic array grows? What constructor? And why would a Drop implementation be invoked to move something? You've moved it, there's nothing left to drop. > Did you use the copy-and-swap idiom properly? I don't believe I'm familiar with this idiom? From some quick googling this seems to be related to panic safety and ensuring that you don't leave things in an invalid state if a panic happens. It doesn't seem to be RAII-specific, and would also apply to a defer mechanism. > Did you define all the "rule of five" methods? Rule of five? You mean that your Clone implementation must properly handle resources in accordance with your Drop implementation, right? I'm not sure where the other three come in?

QuadrupleA 2y ago
I'm speaking about C++, where blind faith in RAII is widespread, so I don't know if Rust's implementation alleviates some of the accidental complexity. But I suspect any system with constructors / destructors leads to a lot of the same implicit behaviors, unintended complications, and leaky abstractions, and I generally favor explicit Initialize() and Cleanup() functions that you call manually, even in languages that support the implicit/magic stuff.
- estebank 2y ago
  Rust doesn't have constructors*. * Well, it kind of does, in so far there is a Ctor enum variant in the compiler implementation to represent the name of a type in the value namespace, but it is not overridable by end users and has no logic.
- Measter 2y ago
  You were conflating details of C++'s object model and implementation of move semantics with RAII. Rust also makes heavy use of RAII, and the details of its object model and move semantics are not the same as C++'s. The only thing that RAII requires is the concept of ownership, and a cleanup function that the compiler knows about. The one implicit thing here is the automatic insertion of calls to the cleanup function.

csb6 2y ago

Rust does not have the rule of five, and it does not really have copy/move constructors. defer does not get you the same benefits as a destructor because you can easily forget to write a defer, while destructors are always called.