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Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

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Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#21

Post by CaptainOfCoit »

macgyverismo wrote: post #2

This borrow checker runs at runtime, which I find not as interesting. Everything starts to look a lot like std::unique_ptr which I think is mostly unneeded as it ads pointer indirection. Could someone explain to me when one would use this? Is it for educational purposes perhaps?

> Could someone explain to me when one would use this? Is it for educational purposes perhaps?

The goal/why is, as almost always, explained in the README:

> rusty.hpp as the time or writing this is a very experimental thing. Its primary purpose is to experiment and test out different coding styles and exploring a different than usual C++ workspace.

TLDR: it's a experiment

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#22

Post by tialaramex »

lorenzhs wrote: post #18
n_plus_1_acc wrote: post #12

Earlier quoted context omitted.

std::optional is fundamentally broken because it has an imolicit conversion (or operator* or something) to T. If you forget to check if it's empty you get UB.

There is no implicit conversion (except to bool, but that tells you whether the optional contains a value), and operator* / operator-> throw std::bad_optional_access if it’s empty. See https://en.cppreference.com/w/cpp/utility/optional

You're describing what it would do in a sane world where WG21 cared about safety.

In this world, as the document you've linked says: "The behavior is undefined if *this does not contain a value."

The operators for such access are actually `noexcept` - the exception you're apparently relying on would be illegal.

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#23

Post by SilasX »

n_plus_1_acc wrote: post #12
cherryteastain wrote: post #7

What's the point of adding Option , Result and Rc/Arc when std::optional, std::expected and std::shared_ptr exist?

std::optional is fundamentally broken because it has an imolicit conversion (or operator* or something) to T. If you forget to check if it's empty you get UB.

Love the typo, and it's fitting here. I'm going to use it for any time the implicit behavior risks burning (immolating) you, as the sibling comments note applies std::optional.

Implicit conversion that immolates: imolicit conversion.

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#24

Post by nly »

tialaramex wrote: post #15
cherryteastain wrote: post #7

What's the point of adding Option , Result and Rc/Arc when std::optional, std::expected and std::shared_ptr exist?

std::optional is a poor shadow of Option. It's what happens when C++ programmers who've seen a Maybe type in a window (years ago by the way, this isn't inspired by Rust, it was just stuck in the standardization process until C++ 17) but are starved of proper types and basic features like pattern matching try to imitate what they saw. As a result for example std::optional doesn't exist, because to a C++ programmer it…

[flagged]

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#25

Post by kzrdude »

tialaramex wrote: post #22
lorenzhs wrote: post #18

Earlier quoted context omitted.

There is no implicit conversion (except to bool, but that tells you whether the optional contains a value), and operator* / operator-> throw std::bad_optional_access if it’s empty. See https://en.cppreference.com/w/cpp/utility/optional

You're describing what it would do in a sane world where WG21 cared about safety. In this world, as the document you've linked says: "The behavior is undefined if *this does not contain a value." The operators for such access are actually `noexcept` - the exception you're apparently relying on would be illegal.

Can we salvage this by forbidding * on optional with compiler warnings (as errors)?

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#26

Post by triblemaster »

nly wrote: post #24
tialaramex wrote: post #15

Earlier quoted context omitted.

std::optional is a poor shadow of Option. It's what happens when C++ programmers who've seen a Maybe type in a window (years ago by the way, this isn't inspired by Rust, it was just stuck in the standardization process until C++ 17) but are starved of proper types and basic features like pattern matching try to imitate what they saw. As a result for example std::optional doesn't exist, because to a C++ programmer it…

[flagged]

You might now want to, but the opinion is correct.

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#27

Post by OtomotO »

nly wrote: post #24
tialaramex wrote: post #15

Earlier quoted context omitted.

std::optional is a poor shadow of Option. It's what happens when C++ programmers who've seen a Maybe type in a window (years ago by the way, this isn't inspired by Rust, it was just stuck in the standardization process until C++ 17) but are starved of proper types and basic features like pattern matching try to imitate what they saw. As a result for example std::optional doesn't exist, because to a C++ programmer it…

[flagged]

Syntax, Schmyntax... I learned too many languages over the years and can't remember every syntax from the top of my head, but does it really matter?

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#28

Post by harry8 »

nly wrote: post #24
tialaramex wrote: post #15

Earlier quoted context omitted.

std::optional is a poor shadow of Option. It's what happens when C++ programmers who've seen a Maybe type in a window (years ago by the way, this isn't inspired by Rust, it was just stuck in the standardization process until C++ 17) but are starved of proper types and basic features like pattern matching try to imitate what they saw. As a result for example std::optional doesn't exist, because to a C++ programmer it…

[flagged]

In 2 sentences this comment encapsulates everything wrong with C++ culture that has caused so many terrible errors becoming standardized forever over the years.

Sometimes being nice really pays off.

Re: Rusty.hpp: A Borrow Checker and Memory Ownership System for C++20

#30

Post by Calavar »

tialaramex wrote: post #15
cherryteastain wrote: post #7

What's the point of adding Option , Result and Rc/Arc when std::optional, std::expected and std::shared_ptr exist?

std::optional is a poor shadow of Option. It's what happens when C++ programmers who've seen a Maybe type in a window (years ago by the way, this isn't inspired by Rust, it was just stuck in the standardization process until C++ 17) but are starved of proper types and basic features like pattern matching try to imitate what they saw. As a result for example std::optional doesn't exist, because to a C++ programmer it…

The lack of support for optional is not an issue at all in my opinion. The actual issue is that std::optional is not a monadic type in the vein of Rust's Option or Haskell's Maybe. So really, what does it buy you over std::pair? Except being unsafe by default since it allows you to access an unconstructed T. Basic monadic operations don't arrive for std::optional until C++23, which is an unforced error. They should have been there from the beginning.
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