Enumerated Types

[Dan Stevens (IAmAI)]

As part of a solution, I wish the value of an attribute to be one of a
finite set of values, in other words I believe I want an 'enumerated
type'. I've look at the 'Enumerable' and 'Enumerator' class and they
appear to me to be unrelated to what I wish to achieve (correct me if
I'm wrong).

I could do the traditional method of named constants with integer
values but I can't help feeling that there must be a class or some
nice method of doing this. Any advice would be appreciated.

 

[Robert Klemme]

As part of a solution, I wish the value of an attribute to be one of a
finite set of values, in other words I believe I want an 'enumerated
type'. I've look at the 'Enumerable' and 'Enumerator' class and they
appear to me to be unrelated to what I wish to achieve (correct me if
I'm wrong).

I could do the traditional method of named constants with integer
values but I can't help feeling that there must be a class or some
nice method of doing this. Any advice would be appreciated.

I believe there are enum classes in the RAA. If you do not want to use
them, symbols come pretty close:

class YourClass
YOUR_ENUM = [
ld,
:young,
:unknown,
].freeze
end

HTH

Kind regards

robert

 

[Dan Stevens (IAmAI)]

It seems to me that I should simply be able to use symbols as values
for my enumerated types, like for example:

class Color

def initialize(color)
@color = color
end

def to_hex
case @color
when :red: 0xFF0000
when :green: 0x00FF00
when :blue: 0x0000FF
else @color
end
end

end

c = Color.newred)
puts c.to_hex.to_s(16)

Might there be any reason why I shouldn't do this, or am I quite fine
doing this?

As part of a solution, I wish the value of an attribute to be one of a
finite set of values, in other words I believe I want an 'enumerated
type'. I've look at the 'Enumerable' and 'Enumerator' class and they
appear to me to be unrelated to what I wish to achieve (correct me if
I'm wrong).

I could do the traditional method of named constants with integer
values but I can't help feeling that there must be a class or some
nice method of doing this. Any advice would be appreciated.

I believe there are enum classes in the RAA. If you do not want to use
them, symbols come pretty close:

class YourClass
YOUR_ENUM = [
ld,
:young,
:unknown,
].freeze
end

HTH

Kind regards

robert

 

[Garance A Drosehn]

As part of a solution, I wish the value of an attribute to be one of a
finite set of values, in other words I believe I want an 'enumerated
type'. I've look at the 'Enumerable' and 'Enumerator' class and they
appear to me to be unrelated to what I wish to achieve (correct me if
I'm wrong).

I could do the traditional method of named constants with integer
values but I can't help feeling that there must be a class or some
nice method of doing this. Any advice would be appreciated.

I picked up this snippet of code:

# -------+---------+---------+-------- + --------+---------+---------+---------+
# Add methods enum and bit_enum to the Object class, thus making it much
# easier and less error-prone to define a long list of constants in a
# class. This idea comes from Ara.T.Howard@noaa, in a posting to ruby-talk
# on August 2, 2005 (in reply to a question). These work very nicely with
# a word-list array as generated via %w(). Very clever!
#
class Object
def enum_constants(*list)
mc = Module === self ? self : self.class
list.flatten.each_with_index{|e, i| mc.const_set e.to_s.intern, i}
end
def enum_bit_constants(*list)
mc = Module === self ? self : self.class
list.flatten.each_with_index{|e, i| mc.const_set e.to_s.intern, 2 ** i}
end
end
# -------+---------+---------+-------- + --------+---------+---------+---------+

An example of using it:

# Constants that define all categories of packets which we recognize.
enum_constants %w(
SBC_NONE SBC_ARRAY SBC_NONUSER SBC_NO_IDSTR
SBC_IGNFAIL SBC_ALL
SBC_UNMATCHED )

The difference between enum_constants() and enum_bit_constants is
that enum_constants will define the values as 1, 2, 3, 4, 5, etc, while
enum_bit_constants will define them as 1,2,4,8,16,32. You can 'or'
the enum_bit_constant values together, and each one is a separate
bit so it won't clobber any other bit constant.

If you are not used to the %w() method of quoting, note that you only
put the names you want in there. You do *not* separate them with
commas!

 

[Robert Klemme]

It seems to me that I should simply be able to use symbols as values
for my enumerated types, like for example:

class Color

def initialize(color)
@color = color
end

def to_hex
case @color
when :red: 0xFF0000
when :green: 0x00FF00
when :blue: 0x0000FF
else @color
end
end

end

c = Color.newred)
puts c.to_hex.to_s(16)

Might there be any reason why I shouldn't do this, or am I quite fine
doing this?

That's perfectly ok. If you need your enums only for mapping then I'd
probably do this:

Color = Struct.new :name do
CODES = Hash.new {|h,k| k}.update(
:red => 0xFF0000,
:green => 0x00FF00
# ...
)

def to_hex; CODES[name] end
end

irb(main):010:0> Color.newred).to_hex.to_s 16
=> "ff0000"

If you need more enum dependent behavior you might want put more complex
objects into the hash instead of only Fixnums.

Kind regards

robert