Show HN: Cppmatch – Rust-Like Pattern Matching and Error Handling for C++ | Hacker News Reader

Show HN: Cppmatch – Rust-Like Pattern Matching and Error Handling for C++

github.com

42 pointsRucadi9 comments

I've created cppmatch, a lightweight, header-only C++ library that brings Rust-inspired pattern matching and error handling to C++.

It tries to imitate the functionality of the questionmark (?) operator in C++ by using a macro that uses the gcc extension https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html

This allows to create exceptionless code with non-intrusive error-as-value that unlike Exceptions, makes it clear which kinds of error a function can generate and forces you to handle (or ignore) them.

The ? operator translates to *expect* To handle the errors I introduce *match* which allows to easily visit the contents of the result or any std::variant (you can use it to imitate rust enums)

You can view an example of this project used in a "real way" in compiler-explorer:

Simplified error types to just be a string: https://compiler-explorer.com/z/6j3866E7W

Multiple structs as error types: https://compiler-explorer.com/z/encbf5f43

Feel free to give feedback or contribute to the project!

Open articleView on HN

https://libfn.org/ also is worth a look.

At a glance, looks good, but it really needs some better documentation! It doesn't seem to include anything similar to this project's expect macro though.

This is great! Thanks for sharing, it is a cool idea to try bringing QoL improvements from Rust to C++. Got a question:

Does this prevent the RVO/NRVO compiler optimizations for return values? And when those fail, same question for the move-construction for types that do have a move constructor.

RVO/NRVO are valid and are not affected.

We are dealing with std::variant, and the move semantics are defined by the alternative. https://en.cppreference.com/w/cpp/utility/variant/operator%3...

Have you considered using the immediately invoked function expression (IIFE) pattern as a standards-compliant alternative to gcc statement expressions?

The main problem with IIFE is the same as with a normal function:

You cannot return the caller function from inside the closure, making the "short-circuit" mechanism provided by questionmark (?) operator not possible.

With the GCC Extension, we get around that using a construct that is pretty similar to IIFE, it allows to return a value from an immediate expression created by a block of code that is surrounded by ({})

The nice thing about this block ({}) is that the last statement is used as the "return value" without an explicit return, this disambiguates between the "expression" return and the "function" return.

Without compiler support, the short-circit is not possible, but with this feature + macros we can create a function that behaves like that.

Regardless of that, the only function that requires this extension is the "except" macro, if you are willing to not short-circuit, you can still use the other functionality of this library.

Makes sense, thank you!

Please leave that Frankenstein of a language alone. Stop bolting features on it, it's already a monster.

Reply on news.ycombinator.com