# class Prism::ASCIISource

Specialized version of `Prism::Source` for source code that includes ASCII characters only. This class is used to apply performance optimizations that cannot be applied to sources that include multibyte characters.

In the extremely rare case that a source includes multi-byte characters but is marked as binary because of a magic encoding comment and it cannot be eagerly converted to UTF-8, this class will be used as well. This is because at that point we will treat everything as single-byte characters.

### Public Instance Methods

character_column (byte_offset)
Source

    # File lib/prism/parse_result.rb, line 243
    def character_column(byte_offset)
      byte_offset - line_start(byte_offset)
    end

Return the column number in characters for the given byte offset.

character_offset (byte_offset)
Source

    # File lib/prism/parse_result.rb, line 238
    def character_offset(byte_offset)
      byte_offset
    end

Return the character offset for the given byte offset.

code_units_cache (encoding)
Source

    # File lib/prism/parse_result.rb, line 260
    def code_units_cache(encoding)
      ->(byte_offset) { byte_offset }
    end

Returns a cache that is the identity function in order to maintain the same interface. We can do this because code units are always equivalent to byte offsets for ASCII-only sources.

code_units_column (byte_offset, encoding)
Source

    # File lib/prism/parse_result.rb, line 267
    def code_units_column(byte_offset, encoding)
      byte_offset - line_start(byte_offset)
    end

Specialized version of ‘code_units_column` that does not depend on `code_units_offset`, which is a more expensive operation. This is essentially the same as `Prism::Source#column`.

code_units_offset (byte_offset, encoding)
Source

    # File lib/prism/parse_result.rb, line 253
    def code_units_offset(byte_offset, encoding)
      byte_offset
    end

Returns the offset from the start of the file for the given byte offset counting in code units for the given encoding.

This method is tested with UTF-8, UTF-16, and UTF-32. If there is the concept of code units that differs from the number of characters in other encodings, it is not captured here.