Collections with values of fixed classes/lengths

ruby-talk
1

Anybody know of any collection (i.e. Array/Hash) classes where
the keys and/or values can be assigned a fixed class? And for
classes that have variable length objects the length be also
potentially fixed across the collection? The main purpose of
doing this would be memory usage. You wouldn't have to store
the class (and possibly object length and pointer to allocated
space) per element and instead just have the raw data in the
collection. You would be able to get the same memory
utilization as C per element if done right.

Here would be a few examples of what I'm talking about and how
much space per element it would take:

- array of Floats (64 bits per element)
- array of N-bit integers (N bits per element)
- hash of 2-character strings (2*8 bits per key and Object per
value)
- array of array of 8 Floats (8*64 bits per line)

For dealing with large data structures, this could be
invaluable for memory usage.

···

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2

I suspect the easiest way is to make a C extension (possibly copying
code from Ruby's array.c and hash.c) that took in a datatype as an
argument to its constructor and malloced etc. based on that.

martin

···

Eric Mahurin <eric_mahurin@yahoo.com> wrote:

Here would be a few examples of what I'm talking about and how
much space per element it would take:

- array of Floats (64 bits per element)
- array of N-bit integers (N bits per element)
- hash of 2-character strings (2*8 bits per key and Object per
value)
- array of array of 8 Floats (8*64 bits per line)

For dealing with large data structures, this could be
invaluable for memory usage.

3

There is no built-in collection that would behave in that manner;
they are heterogenous. Writing an extension to do this should be
fairly trivial, though.

E

···

Le 1/5/2005, "Eric Mahurin" <eric_mahurin@yahoo.com> a écrit:

Anybody know of any collection (i.e. Array/Hash) classes where
the keys and/or values can be assigned a fixed class? And for
classes that have variable length objects the length be also
potentially fixed across the collection? The main purpose of
doing this would be memory usage. You wouldn't have to store
the class (and possibly object length and pointer to allocated
space) per element and instead just have the raw data in the
collection. You would be able to get the same memory
utilization as C per element if done right.

Here would be a few examples of what I'm talking about and how
much space per element it would take:

- array of Floats (64 bits per element)
- array of N-bit integers (N bits per element)
- hash of 2-character strings (2*8 bits per key and Object per
value)
- array of array of 8 Floats (8*64 bits per line)

For dealing with large data structures, this could be
invaluable for memory usage.

--
template<typename duck>
void quack(duck& d) { d.quack(); }

4

You are looking for the String class, which can contain any data you
want. Here's a quick example:

class FloatArray
  def initialize(size=0, filler=0.0)
    @values = ""
    if block_given?
      size.times do |n|
        self << yield(n)
      end
    else
      size.times do
        self << filler
      end
    end
  end
  
  def <<(item)
    @values << [item].pack('F')
    self
  end
  
  def (idx, size=nil)
    if size
      a = FloatArray.new
      val = @values[idx.to_int*4, size*4]
      a.instance_eval{@values = val}
    elsif idx.kind_of? Range
      a = FloatArray.new
      val = @values[idx.min.to_int*4...idx.max.to_i*4]
      a.instance_eval{@values = val}
    else
      @values[idx.to_int*4,4].unpack('F').first
    end
  end
  
  def inspect
    self.class.inspect + @values.unpack('F*').inspect
  end
end

...add a definition for #slice! and one for #insert and you've got
most of the work done making this transparently Arrayish.

cheers,
Mark

···

On 5/1/05, Eric Mahurin <eric_mahurin@yahoo.com> wrote:

Anybody know of any collection (i.e. Array/Hash) classes where
the keys and/or values can be assigned a fixed class? And for
classes that have variable length objects the length be also
potentially fixed across the collection? The main purpose of
doing this would be memory usage. You wouldn't have to store
the class (and possibly object length and pointer to allocated
space) per element and instead just have the raw data in the
collection. You would be able to get the same memory
utilization as C per element if done right.

Here would be a few examples of what I'm talking about and how
much space per element it would take:

- array of Floats (64 bits per element)
- array of N-bit integers (N bits per element)
- hash of 2-character strings (2*8 bits per key and Object per
value)
- array of array of 8 Floats (8*64 bits per line)

For dealing with large data structures, this could be
invaluable for memory usage.

5

Eric Mahurin <eric_mahurin@yahoo.com> writes:

Anybody know of any collection (i.e. Array/Hash) classes where
the keys and/or values can be assigned a fixed class? And for
classes that have variable length objects the length be also
potentially fixed across the collection? The main purpose of
doing this would be memory usage. You wouldn't have to store
the class (and possibly object length and pointer to allocated
space) per element and instead just have the raw data in the
collection. You would be able to get the same memory
utilization as C per element if done right.

Here would be a few examples of what I'm talking about and how
much space per element it would take:

- array of Floats (64 bits per element)
- array of N-bit integers (N bits per element)
- hash of 2-character strings (2*8 bits per key and Object per
value)
- array of array of 8 Floats (8*64 bits per line)

For dealing with large data structures, this could be
invaluable for memory usage.

Shouldn't NArray be good for such things?

···

--
Christian Neukirchen <chneukirchen@gmail.com> http://chneukirchen.org

6

"Eric Mahurin" <eric_mahurin@yahoo.com> schrieb im Newsbeitrag news:20050501180414.24582.qmail@web41115.mail.yahoo.com...

Anybody know of any collection (i.e. Array/Hash) classes where
the keys and/or values can be assigned a fixed class? And for
classes that have variable length objects the length be also
potentially fixed across the collection? The main purpose of
doing this would be memory usage. You wouldn't have to store
the class (and possibly object length and pointer to allocated
space) per element and instead just have the raw data in the
collection. You would be able to get the same memory
utilization as C per element if done right.

Here would be a few examples of what I'm talking about and how
much space per element it would take:

- array of Floats (64 bits per element)
- array of N-bit integers (N bits per element)

For numerics there is for narray:
http://raa.ruby-lang.org/project/narray

- hash of 2-character strings (2*8 bits per key and Object per
value)
- array of array of 8 Floats (8*64 bits per line)

There's also pack and unpack which can be used to implement this.

For dealing with large data structures, this could be
invaluable for memory usage.

"could" or "is"? Do you really know that you need this or is this just guessing?

Kind regards

    robert