Rails源代码分析（35）：ActionController::Routing(6) Segment

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1 Segment的分类

Segment. Abstract Base Class
DynamicSegment. This represents parts of the route that begin with a colon, like :action, :permalink or :id.
ControllerSegment. This is actually a subclass ofDynamicSegment. It represents to special string :controller, because it does some special recognition on those strings. (We’ll cover that more in the next article).
PathSegment. This is for segments that start with an asterisk, and which represent the remainder of the path. Routes like "/file/*path" use a PathSegment.
StaticSegment. This is any static text in your route that must be matched (or generated) verbatim. If you have a path like "/one/two", the strings "one" and "two" are both static segments.
DividerSegment. This is any segment that is used to delimit the other segments. Generally, this will be the forward slash character, but also includes commas, periods, semicolons, and question marks.

2 实现

先看看Segment实现

    class Segment #:nodoc:
      RESERVED_PCHAR = ':@&=+$,;'
      UNSAFE_PCHAR = Regexp.new("[^#{URI::REGEXP::PATTERN::UNRESERVED}#{RESERVED_PCHAR}]", false, 'N').freeze
      attr_accessor :is_optional
      alias_method :optional?, :is_optional
      def initialize
        self.is_optional = false
      end
      def extraction_code
        nil
      end
      # Continue generating string for the prior segments.
      def continue_string_structure(prior_segments)
        if prior_segments.empty?
          interpolation_statement(prior_segments)
        else
          new_priors = prior_segments[0..-2]
          prior_segments.last.string_structure(new_priors)
        end
      end
      def interpolation_chunk
        URI.escape(value, UNSAFE_PCHAR)
      end
      # Return a string interpolation statement for this segment and those before it.
      def interpolation_statement(prior_segments)
        chunks = prior_segments.collect { |s| s.interpolation_chunk }
        chunks << interpolation_chunk
        "/"#{chunks * ''}/"#{all_optionals_available_condition(prior_segments)}"
      end
      def string_structure(prior_segments)
        optional? ? continue_string_structure(prior_segments) : interpolation_statement(prior_segments)
      end
      # Return an if condition that is true if all the prior segments can be generated.
      # If there are no optional segments before this one, then nil is returned.
      def all_optionals_available_condition(prior_segments)
        optional_locals = prior_segments.collect { |s| s.local_name if s.optional? && s.respond_to?(:local_name) }.compact
        optional_locals.empty? ? nil : " if #{optional_locals * ' && '}"
      end
      # Recognition
      def match_extraction(next_capture)
        nil
      end
      # Warning
      # Returns true if this segment is optional? because of a default. If so, then
      # no warning will be emitted regarding this segment.
      def optionality_implied?
        false
      end
    end