Class: Union

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

Overview

The Union class provides an analogue of a C union. Only one member of a Union object can be set to a non-nil value at a time.

Constant Summary collapse

VERSION =

The version of the union library

'1.0.3'

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Union

Creates and returns a new Union. Unlike Struct::Class.new, this does not take any arguments. You must assign attributes individually.

Union.new('Human', :name, :age)
h = Union::Human.new

h.name = 'Daniel' # => #<struct Union::Human name="Daniel", age=nil>
h.age  = 38       # => #<struct Union::Human name=nil, age=38>

– The semantics of Union.new(arg1, arg2, …) would be non-sensical. Which attribute should be set while the rest are ignored? The first one or the last one? I decided to disallow it altogether.



21
22
23
24
25
26
27
28
29
30
31
 
# File 'lib/union.rb', line 21

def initialize
  super
  members.each{ |attribute|
    m = %Q{
      def #{attribute}=(value)
        self['#{attribute}'] = value
      end
    }
    instance_eval(m)
  }
end

Instance Method Details

#[]=(symbol, value) ⇒ Object

Identical to Struct attribute assignment, except that setting one instance variable sets all other instance variables to nil. Also, you cannot use a numeric index. You must use a string or symbol.

Union.new('Human', :name, :age)
h = Union::Human.new

h[:name] = 'Daniel' # => #<struct Union::Human name="Daniel", age=nil>
h[:age]  = 38       # => #<struct Union::Human name=nil, age=38>



43
44
45
46
 
# File 'lib/union.rb', line 43

def []=(symbol, value)
  super(symbol, value)
  members.each{ |m| super(m, nil) unless m.to_s == symbol.to_s }
end