Fiber.[]

(::Symbol) -> untyped

Fiber[key] → value

static VALUE
rb_fiber_storage_aref(VALUE class, VALUE key)
{
    key = rb_to_symbol(key);

    VALUE storage = fiber_storage_get(fiber_current(), FALSE);
    if (storage == Qnil) return Qnil;

    return rb_hash_aref(storage, key);
}

Returns the value of the fiber storage variable identified by key.

The key must be a symbol, and the value is set by Fiber#[]= or Fiber#store.

Ruby version changes

3.2
- Introduce Fiber.[] and Fiber.[]= for inheritable fiber storage. Introduce Fiber#storage and Fiber#storage= (experimental) for getting and resetting the current storage. Introduce Fiber.new(storage:) for setting the storage when creating a fiber. [Feature #19078]
  
  Existing Thread and Fiber local variables can be tricky to use. Thread-local variables are shared between all fibers, making it hard to isolate, while Fiber-local variables can be hard to share. It is often desirable to define unit of execution (“execution context”) such that some state is shared between all fibers and threads created in that context. This is what Fiber storage provides.
  
  Example
```
def log(message)
  puts "#{Fiber[:request_id]}: #{message}"
end

def handle_requests
  while request = read_request
    Fiber.schedule do
      Fiber[:request_id] = SecureRandom.uuid

      request.messages.each do |message|
        Fiber.schedule do
          log("Handling #{message}") # Log includes inherited request_id.
        end
      end
    end
  end
end
```
  You should generally consider Fiber storage for any state which you want to be shared implicitly between all fibers and threads created in a given context, e.g. a connection pool, a request id, a logger level, environment variables, configuration, etc.

See also .[]= .blocking also in 4.1 · 4.0 · 3.3 · 3.2

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