struct Char::Reader

• Char::Reader
• Struct
• Value
• Object

Overview

A Char::Reader allows iterating a String by Chars.

As soon as you instantiate a Char::Reader it will decode the first char in the String, which can be accessed by invoking #current_char. At this point #pos, the current position in the string, will equal zero. Successive calls to #next_char return the next chars in the string, advancing #pos.

NOTE The null character '\0' will be returned in #current_char when the end is reached (as well as when the string is empty). Thus, #has_next? will return false only when #pos is equal to the string's bytesize, in which case #current_char will always be '\0'.

NOTE For performance reasons, Char::Reader has value semantics, so care must be taken when a reader is declared as a local variable and passed to another method:

def lstrip(reader)
  until reader.current_char.whitespace?
    reader.next_char
  end
  reader
end

# caller's internal state is untouched
reader = Char::Reader.new("   abc")
lstrip(reader)
reader.current_char # => ' '

# to modify caller's internal state, the method must return a new reader
reader = lstrip(reader)
reader.current_char # => 'a'

Included Modules

• Enumerable(Char)

Defined in:

Constructors

• .new(string : String, pos = 0)

  Creates a reader with the specified string positioned at byte index pos.

• .new(*, at_end string : String)

  Creates a reader that will be positioned at the last char of the given string.

Instance Method Summary

• #current_char : Char

  Returns the current character, or '\0' if the reader is at the end of the string.

• #current_char? : Char | Nil

  Returns the current character.

• #current_char_width : Int32

  Returns the size of the #current_char (in bytes) as if it were encoded in UTF-8.

• #each(&) : Nil

  Yields successive characters from #string starting from #pos.

• #error : UInt8 | Nil

  If there was an error decoding the current char because of an invalid UTF-8 byte sequence, returns the byte that produced the invalid encoding.

• #has_next? : Bool

  Returns true if the reader is not at the end of the string.

• #has_previous? : Bool

  Returns true if the reader is not at the beginning of the string.

• #next_char : Char

  Reads the next character in the string.

• #next_char? : Char | Nil

  Tries to read the next character in the string.

• #peek_next_char : Char

  Returns the next character in the #string without incrementing #pos.

• #pos : Int32

  Returns the byte position of the current character.

• #pos=(pos : Int32)

  Sets #pos to pos.

• #previous_char : Char

  Reads the previous character in the string.

• #previous_char? : Char | Nil

  Tries to read the previous character in the string.

• #string : String

  Returns the reader's String.

Constructor Detail

Instance Method Detail

reader = Char::Reader.new("ab")
reader.current_char # => 'a'
reader.next_char
reader.current_char # => 'b'
reader.next_char
reader.current_char # => '\0'

reader = Char::Reader.new("aé")
reader.current_char_width # => 1
reader.next_char
reader.current_char_width # => 2

reader = Char::Reader.new("abc")
reader.next_char
reader.each do |c|
  puts c.upcase
end

B
C

reader = Char::Reader.new("ab")
reader.has_next? # => true
reader.next_char # => 'b'
reader.has_next? # => true
reader.next_char # => '\0'
reader.has_next? # => false

reader = Char::Reader.new("abc")
reader.next_char # => 'b'
reader.next_char # => 'c'
reader.next_char # => '\0'
reader.next_char # raise IndexError

reader = Char::Reader.new("abc")
reader.next_char?   # => 'b'
reader.next_char?   # => 'c'
reader.next_char?   # => nil
reader.current_char # => '\0'

reader = Char::Reader.new("ab")
reader.peek_next_char # => 'b'
reader.current_char   # => 'a'

reader = Char::Reader.new("ab")
reader.pos # => 0
reader.next_char
reader.pos # => 1

reader = Char::Reader.new("abc")
reader.next_char
reader.next_char
reader.pos = 0
reader.current_char # => 'a'

reader = Char::Reader.new(at_end: "abc")
reader.previous_char # => 'b'
reader.previous_char # => 'a'
reader.previous_char # raises IndexError

reader = Char::Reader.new(at_end: "abc")
reader.previous_char? # => 'b'
reader.previous_char? # => 'a'
reader.previous_char? # => nil