A library to facilitate on-access conversions of data types based on arbitrary rules.
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Typelib is a way of checking and converting data. It operates as a “filter chain” system which allows it to gradually normalize disparate data into a common type. Each chain is optionally a part of a list which allows it to provide several paths in a single external execution.

The library is arguably very simple and therefore has simple requirements and needs. This is intentional.


Here's a basic example which converts strings OR integers to integers. This sounds anti-climactic, but it allows us to take any kind of integer data and convert it safely.

filters = TypeLib::FilterList.new
check   = proc { |obj| obj.kind_of?(Integer) }
convert = proc { |obj| obj }

check2   = proc { |obj| obj.kind_of?(String) and obj =~ /^\d+$/ }
convert2 = proc { |obj| Integer(obj) }

filters << TypeLib::Filter.new(check, convert)
filters << TypeLib::Filter.new(check2, convert2)

filters.execute(1)     # => 1
filters.execute("1")   # => 1
filters.execute("1.0") # => "1.0"

TypeLib will just not do anything with data it doesn't understand, and return it. This is why the float in this example does nothing – it doesn't match either of the checks.

Filters can also take arguments that propogate into the checks and conversions via TypeLib::Filter#check and TypeLib::Filter#convert. Additionally, these arguments will be passed on from TypeLib::FilterList#execute.

As mentioned prior, TypeLib can also chain. This allows us to say “if this check passes, do/try this, then run this next set of checks/conversions”. This is the foundation of portable conversion, allowing us to sew together many checks and conversions to handle coercing any data into the right type.

In the below check, any integers are converted to strings, and any string that looks like an integer gets coerced to float. Additionally, any string from the start that looks like an integer will also get converted to float. This is reuse of the chain without implying recursion. All parts of TypeLib can be reused at any point within the library's storage.

filters = TypeLib::FilterList.new

check   = proc { |obj| obj.kind_of?(Integer) }
convert = proc { |obj| obj.to_s }

check2   = proc { |obj| obj.kind_of?(String) and obj =~ /^\d+$/ }
convert2 = proc { |obj| obj.to_f }

string_to_float = TypeLib::Filter.new(check2, convert2)

filters << TypeLib::Filter.new(

filters << string_to_float

filters.execute(1)     # => 1.0
filters.execute("1.0") # => 1.0

TypeLib also comes with a (slowly growing) number of canned checks that are optionally available. These are accessible in the 'typelib/canned' library and live in the TypeLib::Canned namespace.


Contributed to design and review of the initial product

  • Dav3xor (David Case)

  • raggi (James Tucker)