`class LazyHash`

A simple hash table which fetches it's values only when required.

Definitions

`def initialize(&block)`

Initialize a lazily loaded hash.

Implementation

def initialize(&block)
	@changed = false
	@values = nil
	
	@loader = block
end

`def [](key)`

Fetch a value by key, loading the hash if necessary.

Signature

parameter　key　Object: The key.
returns　Object | Nil: The value.

Implementation

def [] key
	load![key]
end

`def []=(key, value)`

Store a value by key.

Signature

parameter　key　Object: The key.
parameter　value　Object: The value.
returns　Object: The stored value.

Implementation

def []= key, value
	values = load!
	
	if values[key] != value
		values[key] = value
		@changed = true
	end
	
	return value
end

`def include?(key)`

Check whether the hash contains a key.

Signature

parameter　key　Object: The key.
returns　Boolean: Whether the key exists.

Implementation

def include?(key)
	load!.include?(key)
end

`def delete(key)`

Delete a value by key.

Signature

parameter　key　Object: The key.
returns　Object | Nil: The deleted value.

Implementation

def delete(key)
	load!
	
	@changed = true if @values.include? key
	
	@values.delete(key)
end

`def changed?`

Check whether any value has changed.

Signature

returns　Boolean: Whether the hash has changed.

Implementation

def changed?
	@changed
end

`def now`

The current time for session expiry and persistence.

Signature

returns　Time: The current time in UTC.

Implementation

def now
	Time.now.utc
end

`def persist(timeout = nil)`

Persist the session values if they have changed or require updating.

Signature

parameter　timeout　Numeric | Nil: The maximum age before an update is required.
yields　{|values, updated_at| ...}: The loaded values and their update time.
returns　Object | Nil: The result of the block if persistence was required.

Implementation

def persist(timeout = nil)
	return unless needs_update?(timeout)
	
	values = load!
	updated_at = values[:updated_at] = now
	
	result = yield(values, updated_at)
	@changed = false
	
	return result
end

`def loaded?`

Check whether the underlying values have been loaded.

Signature

returns　Boolean: Whether the values are loaded.

Implementation

def loaded?
	!@values.nil?
end

`def needs_update?(timeout = nil)`

Check whether the values should be persisted.

Signature

parameter　timeout　Numeric | Nil: The maximum age before an update is required.
returns　Boolean: Whether an update is required.

Implementation

def needs_update?(timeout = nil)
	# If data has changed, we need update:
	return true if @changed
	
	# We want to be careful here and not call load! which isn't cheap operation.
	if timeout and @values and updated_at = @values[:updated_at]
		# If the last update was too long ago, we need update:
		return true if updated_at < (now - timeout)
	end
	
	return false
end

`def load!`

Load and return the underlying values.

Implementation

def load!
	@values ||= @loader.call(now)
end