[librecat-dev] Message for Catmandu::Bind implementers

Patrick Hochstenbach Patrick.Hochstenbach at UGent.be
Thu Jun 29 15:06:53 CEST 2017

Dear all

In Catmandu 1.06 processing of some Catmandu::Bind-s can be made faster by giving them the role ‘Catmandu::Fix::Bind::Group’.
Instead of writing in the Perl module for a Bind:

    with 'Catmandu::Fix::Bind’;


    with 'Catmandu::Fix::Bind', 'Catmandu::Fix::Bind::Group’;

What does this do?

When you have a Bind in a Fix script like:



Then Catmandu will first execute the `unit` method of the Bind and then execute `bind` on all fixes found in the Bind block. Given `data` as the currrent item that needs to be processed, in pseudo code this Bind block  looks like:

  m_data = mybinder->unit(data)
  m_data = mybinder->bind(m_data, fix1)
  m_data = mybinder->bind(m_data, fix2)
  m_data = mybinder->bind(m_data, fix3)
  data      = mybinder->result(m_data)

When the `mybinder` has the role Catmandu::Fix::Bind::Group all the fixes in the Bind block wll be executed as one grouped anonymous function:

  m_data = mybinder->unit(data)
  m_data = mybinder->bind(m_data, sub { fix1; fix2; fix3 })
  data      = mybinder->result(m_data)

When you don’t need to explicitly run the ‘->bind’ on each separate fix in a Bind block then you want to use this Group role (probably is most Binds now available)

One counterexample where you don’t want Groups is for example the `maybe()` Bind which skips faulty fixes:

  m_data = maybe->unit(data)
  m_data = maybe->bind(m_data, fix1) # ok
  m_data = maybe->bind(m_data, fix2) # dies and ignored
  m_data = maybe->bind(m_data, fix3) # ignored because the previous was ignored
  data      = maybe->result(m_data)


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