Module: Constants::Stash

Included in:
ConstantLibrary::Collection, ConstantLibrary::Index
Defined in:
lib/constants/stash.rb

Overview

Stash provides methods to store values by a non-unique key. The initial stored value is directly stored by the key, subsequent values are grouped into a StashArray.

class StashingHash < Hash
  include Constants::Stash

  def initialize(*args)
    super(*args)
    @nil_value = nil
  end
end

s = StashingHash.new

s.stash('key', 'one')
s['key']                # => 'one'

s.stash('key', 'two')
s['key']                # => ['one' , 'two']
s['key'].class          # => Constants::Stash::StashArray

The stash method requires some kind of flag to differentiate when a new value should be stored and when the existing value and new value should be converted into a StashArray. If the existing value as determined by [] is equal to the nil_value, then the new value is stored through []=.

s = StashingHash.new
s['key']                # => nil    
s.nil_value             # => nil

s.stash('key', 1)
s['key']                # => 1

s.stash('key', 2)
s['key']                # => [1, 2]

In the first case, the existing value for ‘key’ is equals the nil_value, so the new value is set. In the second case, the existing value for ‘key’ does not equal the nil_value; stash takes this as a signal that a non-unique key was specified and collects the values into a StashArray. As a consequence, neither the nil_value nor StashArrays may be stashed.

s.stash('key', nil)   # ! ArgumentError

Defined Under Namespace

Classes: StashArray

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#nil_value ⇒ Object

The value considered to be nil in store (used to signal when a new value can be stashed for a given key; if store == nil_value, then a new value can be stashed).



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# File 'lib/constants/stash.rb', line 61

def nil_value
  @nil_value
end

Instance Method Details

#stash(key, value) ⇒ Object

Assigns the value to key in store. If the store already has a non-nil_value at key (as determined by []), then the existing and new value will be concatenated into a StashArray. All subsequent values are added to the StashArray. stash uses the []= method to set values.

nil_value and StashArray values cannot be stashed; either raises an error.



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# File 'lib/constants/stash.rb', line 71

def stash(key, value)
  case value
  when nil_value
    raise ArgumentError.new("the nil_value for self cannot be stashed")
  when StashArray
    raise ArgumentError.new("StashArrays cannot be stashed")
  end
  
  current_value = self[key]
  
  case current_value
  when nil_value
    self[key] = value
  when StashArray
    current_value << value
  else
    self[key] = StashArray.new([current_value, value])
  end
  
  self
end