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# Provides a numbering object that will produce letters. Accepts four
# options for numbering that will control how the letters are presented
# when given as #[](index). This numbering object will only provide 26
# values ("a" .. "z") unless :wrap is +true+.
#
# <tt>:transform</tt>:: The symbol representing the method to be called on
# the letter. This must be a method that does not
# require any arguments.
# <tt>:postfix</tt>:: The value that will be appended to the letter
# presented by #[]. Defaults to +nil+.
# <tt>:prefix</tt>:: The value that will be prepended to the letter
# presented by #[]. Defaults to +nil+.
# <tt>:wrap</tt>:: If +true+, then indexes will be wrapped from "z"
# to "a".
#
# a1 = Text::Format::Alpha.new(:postfix => ".")
# puts a1[0] # => "a."
# puts a1[1] # => "b.
# puts a1[27] # => ""
#
# a2 = Text::Format::Alpha.new(:prefix => "A.")
# puts a2[0] # => "A.a"
# puts a2[1] # => "A.b"
# puts a2[27] # => ""
#
# a3 = Text::Format::Alpha.new(:transform => :upcase)
# puts a3[0] # => "A"
# puts a3[1] # => "B"
# puts a3[27] # => ""
#
# a4 = Text::Format::Alpha.new(:wrap => true)
# puts a4[0] # => "a"
# puts a4[27] # => "b"
class Text::Format::Alpha
def [](index)
if @wrap
ltr = (?a + (index % 26)).chr
elsif index.between?(0, 25)
ltr = (?a + index).chr
else
ltr = nil
end
if ltr
if @transform
"#{@prefix}#{ltr.send(transform)}#{@postfix}"
else
"#{@prefix}#{ltr}#{@postfix}"
end
else
""
end
end
def initialize(options = {}) #:yields self:
@transform = options[:transform] || nil
@wrap = options[:wrap] || false
@postfix = options[:postfix] || nil
@prefix = options[:prefix] || nil
end
end
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