Class: LazyString

Inherits:
Object
  • Object
show all
Defined in:
lib/lazy_string.rb

Overview

LazyString is a class for computing strings only when necessary. This is useful when computing the string is expensive but the string is unlikely to be used: an error message passed as an argument, for example.

Constant Summary collapse

VERSION =

The version string.

'0.4.0'

Instance Method Summary collapse

Constructor Details

#initialize(&block) ⇒ LazyString

Creates a new lazy string. The block argument will be saved for later use by #to_str. If no block argument is given, it will default to a block that returns an empty string.



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# File 'lib/lazy_string.rb', line 17

def initialize(&block)
  @block = block || lambda { '' }
end

Instance Method Details

#to_s ⇒ Object

A synonym for #to_str.



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# File 'lib/lazy_string.rb', line 24

def to_s
  to_str
end

#to_str ⇒ Object

Returns the computed string. It will compute the string by calling (with no arguments) the block passed to ::new. If the block's return value responds to the to_str message, to_str will be sent to it to create the string. Otherwise, to_s will be sent to it. The computed string will be saved, so subsequent invocations of this method will not cause the block to be called again.



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# File 'lib/lazy_string.rb', line 36

def to_str
  @str ||= begin
    result = @block.call
    if result.respond_to?(:to_str)
      result.to_str
    else
      result.to_s
    end
  end
end