Rustlang - sgml/signature GitHub Wiki

Runtime

• https://doc.rust-lang.org/reference/runtime.html
• https://www.osohq.com/post/rust-reflection-pt-1

Rust vs C++

Scenario / Use Case	Why Replacing C++ With Rust Is Too Risky
Hard real‑time systems (RTOS, avionics, medical devices)	Rust lacks proven WCET analysis; LLVM optimizations introduce timing nondeterminism; certification toolchains are immature.
Systems requiring stable ABI	Rust has no stable ABI; long‑term binary compatibility for plugins, shared libraries, or kernel modules cannot be guaranteed.
Large legacy C++ codebases	Deep template metaprogramming, custom allocators, and undocumented invariants make rewrites expensive and destabilizing.
Vendor‑locked toolchain environments	Automotive, aerospace, and industrial systems rely on certified C++ compilers that Rust cannot replace without losing certification or support.
GPU programming (CUDA, HIP/ROCm, Metal)	GPU ecosystems are tightly coupled to C++; Rust GPU tooling is experimental and lacks vendor‑level debugging/profiling.
Memory‑constrained embedded systems	Rust monomorphization and safety abstractions can increase binary size and stack usage beyond microcontroller limits.
Deterministic destruction requirements	C++ RAII provides strict destruction timing; Rust’s drop semantics follow ownership rules that may not match required cleanup order.
Systems with decades of domain knowledge	Rewrites risk losing subtle performance hacks, undocumented behavior, and institutional knowledge embedded in C++ code.
Safety‑critical cryptography	Mature C++ crypto libraries have long verification histories; Rust crypto depends on LLVM optimizations that may break constant‑time guarantees.
Ultra‑low‑latency trading systems	Nanosecond‑level latency budgets can be disrupted by Rust’s abstraction overhead, register pressure, or inlining unpredictability.
Kernel or hypervisor development	Rust kernel support is emerging; unsafe‑block auditing, debugging, and tooling are less mature than C++ equivalents.
Long‑term maintenance environments	Industries requiring 20–40 year support windows cannot rely on Rust’s rapidly evolving ecosystem; C++ offers stable standards and frozen toolchains.

Porting C

HTTPD Integration

use apache2::server::{APRSuccess, HTTP_MOVED_PERMANENTLY};
use apache2::{ApacheModule, Request, Status};

pub struct RedirectModule;

impl ApacheModule for RedirectModule {
    fn handler(r: &mut Request) -> Status {
        if r.uri().starts_with("/old-path") {
            r.headers_out().add("Location", "http://example.com/new-path");
            r.set_status(HTTP_MOVED_PERMANENTLY);
            return Status::DONE; // Complete handling for the request
        }
        Status::DECLINED // Let other handlers process the request
    }
}

Installer

cargo add apache2

Build

cargo build --release

httpd.conf

LoadModule redirect_module /usr/lib/apache2/modules/mod_redirect.rs.so
```

#### mod_test

t/TEST -start t/TEST -run

## Projects
```
tools:
  text_editors:
    - name: "Zed"
      url: "https://zed.dev"
    - name: "Helix"
      url: "https://helix-editor.com"
    - name: "Lapce"
      url: "https://lapce.dev"
    - name: "Kibi"
      url: "https://github.com/ilai-deutel/kibi"
  ides:
    - name: "Lapce"
      url: "https://lapce.dev"
    - name: "Zed"
      url: "https://zed.dev"
  email_clients:
    - name: "Himalaya"
      url: "https://github.com/pimalaya/himalaya"
    - name: "Lettre"
      url: "https://docs.rs/lettre/latest/lettre/"
    - name: "Email-lib"
      url: "https://docs.rs/email-lib"
  rest_clients:
    - name: "Reqwest"
      url: "https://github.com/seanmonstar/reqwest"
    - name: "Hyper"
      url: "https://hyper.rs"
    - name: "Surf"
      url: "https://github.com/http-rs/surf"
```

## Compiletime

* https://www.shuttle.rs/blog/2022/12/23/procedural-macros
* https://tembo.io/blog/postgres-extension-in-rust-pgmq

## Complexity

Closures & Lambdas: The Rust idiom `let add = |x, y| x + y;` uses an anonymous function with environment capture, which cannot be mapped to another language that does not implement this natively.

Pattern Matching: Rust's match statement supports deep pattern matching (with nested or complex patterns) that has no direct counterpart with `IF...ELSE` or `SELECT CASE...WHEN`. A regex approach would fail to capture nested patterns reliably.

Generics and Trait Bounds: complex type inference and compile‑time checking cannot be simply mapped from Rust to another language.

Async/Await Patterns: asynchronous primitives cannot be mapped to a synchronous execution model.

Macros: Compile‑time code generation cannot be mapped to another language.

Unsafe Blocks & Pointer Arithmetic: Pointer memory operations cannot be mapped to another language.

## Assertion

Rust assertions can be disabled by the `debug_assert!` macro.

## Rust for Basic Devs
| Regex                             | Rust Code                          | QBasic Code                |
|-----------------------------------|------------------------------------|----------------------------|
| `let (\w+) = (.+);`               | `let x = 42;`                      | `x = 42`                   |
| `println!\("(.*)"\);`             | `println!("Hello, world!");`        | `PRINT "Hello, world!"`    |
| `fn (\w+)\(.*\) {`                | `fn add(a: i32, b: i32) {`           | `FUNCTION add(a, b)`        |