Solidus - A safe Rust library for writing Ruby extensions

Solidus provides automatic stack pinning of Ruby values, eliminating the need for users to manually ensure values stay on the stack. This prevents undefined behavior that can occur when Ruby values are accidentally moved to the heap.

Safety Model

Ruby's garbage collector scans the C stack to find live VALUE references. If a VALUE is moved to the heap (e.g., into a Vec or Box), the GC cannot see it and may collect the underlying Ruby object, leading to use-after-free bugs.

Solidus solves this with compile-time enforcement:

• Method arguments use Pin<&StackPinned<T>> which cannot be moved to the heap
• Explicit BoxValue<T> for heap storage registers values with Ruby's GC
• Immediate values (Fixnum, Symbol, true, false, nil) bypass pinning as they don't need GC protection

Core Types

• [Value] - Base wrapper around Ruby's VALUE
• StackPinned<T> - !Unpin wrapper for stack pinning
• [BoxValue<T>] - Heap-allocated, GC-registered wrapper
• [Ruby] - Handle to the Ruby VM
• [Error] - Ruby exception wrapper

Example

use solidus::prelude::*;

fn concat(rb_self: RString, other: Pin<&StackPinned<RString>>) -> Result<RString, Error> {
    // `other` is guaranteed to be on the stack - enforced by the type system
    rb_self.concat(other.get())
}