TypedCache

TypedCache is a lightweight, type-safe façade around your favourite Ruby cache stores. It adds three things on top of the raw back-end implementation:

1. Namespacing – hierarchical Namespace helpers prevent key collisions. You can create nested namespaces easily, like Namespace.at("users", "profiles", "avatars").
2. Stronger types – RBS signatures as well as monadic types like Either, Maybe, and Snapshot wrap cache results so you always know whether you have a value, an error, or a cache-miss.
3. Composable decorators – behaviours like instrumentation can be layered on without touching the underlying store.

TL;DR – Think Faraday or Rack middlewares, but for caching.

bundle add typed_cache && bundle install
# or
gem install typed_cache

This gem does is also cryptographically signed, if you want to ensure the gem was not tampered with, make sure to use these commands:

bundle add typed_cache && bundle install --trust-policy=HighSecurity
# or
gem install typed_cache -P HighSecurity

If there are issues with unsigned gems, use MediumSecurity instead.

require "typed_cache"

# 1. Build a store
store = TypedCache.builder
  .with_backend(:memory, shared: true)
  .with_instrumentation(:rails) # e.g. using ActiveSupport
  .build
  .value # unwrap Either for brevity

# 2. Get a reference to a key
user_ref = store.ref("users:123") # => CacheRef

# 3. Fetch and compute if absent
user_snapshot = user_ref.fetch do
  puts "Cache miss! Computing..."
  { id: 123, name: "Jane" }
end.value # => Snapshot

puts "Found: #{user_snapshot.value} (from_cache?=#{user_snapshot.from_cache?})"

• Back-end (TypedCache::Backend) – persists data (Memory, Redis, etc.).
• Decorator (TypedCache::Decorator) – wraps an existing store to add behaviour (Instrumentation, Logging, Circuit-Breaker …).

Both include the same public Store interface, so they can be composed freely. Registries keep them separate:

TypedCache::Backends.available   # => [:memory, :active_support]
TypedCache::Decorators.available # => [:instrumented]

class RedisBackend
  include TypedCache::Backend
  # … implement #get, #set, etc.
end

TypedCache::Backends.register(:redis, RedisBackend)

class LogDecorator
  include TypedCache::Decorator
  def initialize(store) = @store = store
  def set(key, value)
    puts "[cache] SET #{key}"
    @store.set(key, value)
  end
  # delegate the rest …
end

TypedCache::Decorators.register(:logger, LogDecorator)

All operations return one of:

• Either.right(Snapshot) – success
• Either.left(CacheMissError) – key not present
• Either.left(StoreError) – transport / serialization failure

Use the monad directly or pattern-match:

result.fold(
  ->(err)      { warn err.message },
  ->(snapshot) { puts snapshot.value },
)

While you can call get, set, and fetch directly on the store, the more powerful way to work with TypedCache is via the CacheRef object. It provides a rich, monadic API for a single cache key. The Store also provides fetch_all for batch operations.

You get a CacheRef by calling store.ref(key):

user_ref = store.ref("users:123") # => #<TypedCache::CacheRef ...>

Now you can operate on it:

# Fetch a value, computing it if it's missing
snapshot_either = user_ref.fetch do
  { id: 123, name: "Jane Doe" }
end

# The result is always an Either[Error, Snapshot]
snapshot_either.fold(
  ->(err)      { warn "Something went wrong: #{err.message}" },
  ->(snapshot) { puts "Got value: #{snapshot.value} (from cache: #{snapshot.from_cache?})" }
)

# You can also map over values
name_either = user_ref.map { |user| user[:name] }
puts "User name is: #{name_either.value.value}" # unwrap Either, then Snapshot

For retrieving multiple keys at once, the Store provides a fetch_all method. This is more efficient than fetching keys one by one, especially with remote back-ends like Redis.

It takes a list of keys and a block to compute the values for any missing keys.

user_refs = store.fetch_all("users:123", "users:456") do |missing_key|
  # This block is called for each cache miss
  user_id = missing_key.split(":").last
  puts "Cache miss for #{missing_key}! Computing..."
  { id: user_id, name: "Fetched User #{user_id}" }
end

user_refs.each do |key, snapshot_either|
  snapshot_either.fold(
    ->(err)      { warn "Error for #{key}: #{err.message}" },
    ->(snapshot) { puts "Got value for #{key}: #{snapshot.value}" }
  )
end

The CacheRef API encourages a functional style and makes composing cache operations safe and predictable.

TypedCache can publish events about cache operations using different instrumenters. To enable it, use the with_instrumentation method on the builder, specifying an instrumentation backend:

# For ActiveSupport::Notifications (e.g. in Rails)
store = TypedCache.builder
  .with_backend(:memory)
  .with_instrumentation(:rails)
  .build.value

# For Dry::Monitor
store = TypedCache.builder
  .with_backend(:memory)
  .with_instrumentation(:dry)
  .build.value

Events are published to a topic like typed_cache.<operation> (e.g., typed_cache.get). The topic namespace can be configured.

Payload keys include: :namespace, :key, :operation, :duration, and cache_hit.

You can subscribe to these events like so:

# Example for ActiveSupport
ActiveSupport::Notifications.subscribe("typed_cache.get") do |name, start, finish, id, payload|

# Or you can subscribe via the store object itself
instrumenter = store.instrumenter
instrumenter.subscribe("get") do |event|
  payload = event.payload
  puts "Cache GET for key #{payload[:key]} took #{payload[:duration]}ms. Hit? #{payload[:cache_hit]}"
end

If you call with_instrumentation with no arguments, it uses a Null instrumenter, which has no overhead.

Just like with back-ends and decorators, you can write and register your own instrumenters. An instrumenter must implement an instrument and a subscribe method.

class MyCustomInstrumenter
  include TypedCache::Instrumenter

  def instrument(operation, key, **payload, &block)
    # ... your logic ...
  end

  def subscribe(event_name, **filters, &block)
    # ... your logic ...
  end
end

# Register it
TypedCache::Instrumenters.register(:custom, MyCustomInstrumenter)

# Use it
store = TypedCache.builder
  .with_instrumentation(:custom)
  # ...

For more advanced scenarios—including Rails integration, pattern matching, custom back-ends, and testing—see examples.md.

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