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Nanoc::Filter

Nanoc::Filter is responsible for filtering items. It is the superclass for all textual filters.

A filter instance should only be used once. Filters should not be reused since they store state.

When creating a filter with a hash containing assigned variables, those variables will be made available in the `@assigns` instance variable and the {assigns} method. The assigns itself will also be available as instance variables and instance methods.

@example Accessing assigns in different ways

filter = SomeFilter.new({ :foo => 'bar' })
filter.instance_eval { @assigns[:foo] }
  # => 'bar'
filter.instance_eval { assigns[:foo] }
  # => 'bar'
filter.instance_eval { @foo }
  # => 'bar'
filter.instance_eval { foo }
  # => 'bar'

@abstract Subclass and override {run} to implement a custom filter.

Constants

TMP_BINARY_ITEMS_DIR

The path to the directory where temporary binary items are stored

Attributes

assigns[R]

A hash containing variables that will be made available during filtering.

@return [Hash]

Public Class Methods

from_binary?() click to toggle source

@return [Boolean] True if this filter can be applied to binary item

representations, false otherwise
# File lib/nanoc/base/compilation/filter.rb, line 69
def from_binary?
  (@from || :text) == :binary
end
new(hash={}) click to toggle source

Creates a new filter that has access to the given assigns.

@param [Hash] hash A hash containing variables that should be made

available during filtering.
# File lib/nanoc/base/compilation/filter.rb, line 110
def initialize(hash={})
  @assigns = hash
  super
end
requires(*requires) click to toggle source

@overload requires(*requires)

Sets the required libraries for this filter.
@param [Array<String>] requires A list of library names that are required
@return [void]

@overload requires

Returns the required libraries for this filter.
@return [Enumerable<String>] This filter’s list of library names that are required
# File lib/nanoc/base/compilation/filter.rb, line 86
def requires(*requires)
  if requires.size > 0
    @requires = requires
  else
    @requires || []
  end
end
setup() click to toggle source

Requires the filter’s required library if necessary.

@return [void]

# File lib/nanoc/base/compilation/filter.rb, line 97
def setup
  @setup ||= begin
    self.requires.each { |r| require r }
    true
  end
end
to_binary?() click to toggle source

@return [Boolean] True if this filter results in a binary item

representation, false otherwise
# File lib/nanoc/base/compilation/filter.rb, line 75
def to_binary?
  (@to || :text) == :binary
end
type(arg) click to toggle source

Sets the new type for the filter. The type can be `:binary` (default) or `:text`. The given argument can either be a symbol indicating both “from” and “to” types, or a hash where the only key is the “from” type and the only value is the “to” type.

@example Specifying a text-to-text filter

type :text

@example Specifying a text-to-binary filter

type :text => :binary

@param [Symbol, Hash] arg The new type of this filter

@return [void]

# File lib/nanoc/base/compilation/filter.rb, line 59
def type(arg)
  if arg.is_a?(Hash)
    @from, @to = arg.keys[0], arg.values[0]
  else
    @from, @to = arg, arg
  end
end

Public Instance Methods

depend_on(items) click to toggle source

Creates a dependency from the item that is currently being filtered onto the given collection of items. In other words, require the given items to be compiled first before this items is processed.

@param [Array<Nanoc::Item>] items The items that are depended on.

@return [void]

# File lib/nanoc/base/compilation/filter.rb, line 182
def depend_on(items)
  # Notify
  items.each do |item|
    Nanoc::NotificationCenter.post(:visit_started, item)
    Nanoc::NotificationCenter.post(:visit_ended,   item)
  end

  # Raise unmet dependency error if necessary
  items.each do |item|
    rep = item.reps.find { |r| !r.compiled? }
    raise Nanoc::Errors::UnmetDependency.new(rep) if rep
  end
end
filename() click to toggle source

Returns the filename associated with the item that is being filtered.

It is in the format `item <identifier> (rep <name>)`.

@return [String] The filename

# File lib/nanoc/base/compilation/filter.rb, line 165
def filename
  if assigns[:layout]
    "layout #{assigns[:layout].identifier}"
  elsif assigns[:item]
    "item #{assigns[:item].identifier} (rep #{assigns[:item_rep].name})"
  else
    '?'
  end
end
output_filename() click to toggle source

Returns a filename that is used to write data to. This method is only

used on binary items. When running a binary filter on a file, the
resulting file must end up in the location returned by this method.

The returned filename will be absolute, so it is safe to change to

another directory inside the filter.

@return [String] The output filename

# File lib/nanoc/base/compilation/filter.rb, line 150
def output_filename
  @output_filename ||= begin
    FileUtils.mkdir_p(TMP_BINARY_ITEMS_DIR)
    tempfile = Tempfile.new('', TMP_BINARY_ITEMS_DIR)
    new_filename = tempfile.path
    tempfile.close!

    File.expand_path(new_filename)
  end
end
run(content_or_filename, params={}) click to toggle source

Runs the filter on the given content or filename.

@abstract

@param [String] content_or_filename The unprocessed content that should

be filtered (if the item is a textual item) or the path to the file
that should be filtered (if the item is a binary item)

@param [Hash] params A hash containing parameters. Filter subclasses can

use these parameters to allow modifying the filter's behaviour.

@return [String, void] If the filter output binary content, the return

value is undefined; if the filter outputs textual content, the return
value will be the filtered content.
# File lib/nanoc/base/compilation/filter.rb, line 138
def run(content_or_filename, params={})
  raise NotImplementedError.new("Nanoc::Filter subclasses must implement #run")
end
setup_and_run(*args) click to toggle source

Sets up the filter and runs the filter. This method passes its arguments to {run} unchanged and returns the return value from {run}.

@see {run}

# File lib/nanoc/base/compilation/filter.rb, line 119
def setup_and_run(*args)
  self.class.setup
  self.run(*args)
end

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