For future reference these are some API design ideas- not working code!

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Java API ideas
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http://www.ioplex.com/~miallen/encdec/  (binary pack/unpack utilities)

The Java API would take an object, and a list of field  names, then use the
Java Reflection API to read or write those fields  during packing and
unpacking.

I.e. if you are going to unpack a tpl with format string A(if), you  
might create a Java class that has two instance variables (an int and  
a double). Then you create an object of that class, and pass it to  
tpl_map (or perhaps a constructor for the Tpl class), like

class Unpacker {
        int count;
        double weight;
}
... 
Unpacker up = new Unpacker();
Tpl tn = new Tpl("A(if)", up, "count", "weight");
tn.tpl_unpack(1);  // stores unpacked values into count,weight using Reflection

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Ruby API ideas
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#!/usr/local/ruby/bin/ruby -w

class Tpl < Hash
       def initialize(fmt, *args)
         @fmt = fmt
         @args = args
       end

       def pack
         @args.each {|key| puts "#{key} #{self[key]}"}
       end
end


p = Tpl.new("A(i)", :id);
10.times do |i|
   p[:id] = i
   p.pack
end
p.dump("/tmp/file.tpl")  # p.dump(arg) checks arg.respond_to?(:write)

p = Tpl.new("A(i)", :id);
p.load("/tmp/file.tpl")
p.unpack(1) {|h| puts h[:id]}