From: vikrambkumar@...
Date: 2008-07-14T05:40:38+09:00
Subject: Methods with [] braces can't take block arguments?

Hi All,

I want to create a L2 cache object based on Hash.

Since it's a secondary cache, the object bound to the key may have
expired, but can be recreated.

However I want the get method itself to do get-get-set if the "value"
object has expired. Check the class definition:

#---------
class L2Cache
  # use Hash for the store
  def initialize
    @h = Hash.new
  end

  # try the hash.. if not found and a block
  # to recreate is provided, create the value
  # and bind it again
  def get(key)
    value = @h[key]
    if value.nil? && block_given?
      puts "value is nil but recreating it using the block" if $DEBUG
      value = self[key] = yield
    elsif value.nil?
      puts "value is nil but not recreate block found" if $DEBUG
    end
    value
  end

  # proxy to hash
  def [](key)
    @h[key]
  end

  # proxy to hash
  def []=(key, value)
    @h[key] = value
  end
end
#---------

c = L2Cache.new
c[:k]                    # >> nil
c.get(:k) { "foo"}       #>> foo
c[:foo]                  # >> foo

#----------------

However I cannot make the the default get method using [] take a block
as an argument.

If I define the method as:
#--------
  def [](key)
    value = @h[key]
    if value.nil? && block_given?
      puts "value is nil but recreating it using the block"
      value = self[key] = yield
    elsif value.nil?
      puts "value is nil but not recreate block found"
    end
    value
  end
#--------

I can't use c[:k] { block here }

#--------
c = L2Cache.new
c[:k]                 # >> nil
c.[:k] { "foo"}       # >> syntax error, unexpected '{', expecting
$end
#--------

Is there a way to make methods names with special characters take
block arguments?