class StringScanner

Overview

StringScanner provides for lexical scanning operations on a String.

Example

require "string_scanner"

s = StringScanner.new("This is an example string")
s.eos? # => false

s.scan(/\w+/) # => "This"
s.scan(/\w+/) # => nil
s.scan(/\s+/) # => " "
s.scan(/\s+/) # => nil
s.scan(/\w+/) # => "is"
s.eos?        # => false

s.scan(/\s+/) # => " "
s.scan(/\w+/) # => "an"
s.scan(/\s+/) # => " "
s.scan(/\w+/) # => "example"
s.scan(/\s+/) # => " "
s.scan(/\w+/) # => "string"
s.eos?        # => true

s.scan(/\s+/) # => nil
s.scan(/\w+/) # => nil

Scanning a string means remembering the position of a scan offset, which is just an index. Scanning moves the offset forward, and matches are sought after the offset; usually immediately after it.

Method Categories

Methods that advance the scan offset:

Methods that look ahead:

Methods that deal with the position of the offset:

Methods that deal with the last match:

Miscellaneous methods:

Defined in:

string_scanner.cr

Constructors

Instance Method Summary

Instance methods inherited from class Reference

==(other : self)
==(other) ==, dup dup, hash hash, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference)
same?(other : Nil) same?, to_s(io : IO) : Nil to_s

Constructor methods inherited from class Reference

new new

Instance methods inherited from class Object

!=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, class class, dup dup, hash hash, inspect(io : IO)
inspect inspect, itself itself, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, tap(&block) tap, to_json(io : IO)
to_json to_json, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ") to_pretty_json, to_s
to_s(io : IO) to_s, to_yaml(io : IO)
to_yaml to_yaml, try(&block) try, unsafe_as(type : T.class) forall T unsafe_as

Constructor methods inherited from class Object

from_json(string_or_io, root : String) : self
from_json(string_or_io) : self from_json, from_yaml(string_or_io) : self from_yaml

Constructor Detail

def self.new(str : String) #

View source

Instance Method Detail

def [](n) #

Returns the n-th subgroup in the most recent match.

Raises an exception if there was no last match or if there is no subgroup.

s = StringScanner.new("Fri Dec 12 1975 14:39")
regex = /(?<wday>\w+) (?<month>\w+) (?<day>\d+)/
s.scan(regex) # => "Fri Dec 12"
s[0]          # => "Fri Dec 12"
s[1]          # => "Fri"
s[2]          # => "Dec"
s[3]          # => "12"
s["wday"]     # => "Fri"
s["month"]    # => "Dec"
s["day"]      # => "12"

View source
def []?(n) #

Returns the nilable n-th subgroup in the most recent match.

Returns nil if there was no last match or if there is no subgroup.

s = StringScanner.new("Fri Dec 12 1975 14:39")
regex = /(?<wday>\w+) (?<month>\w+) (?<day>\d+)/
s.scan(regex)  # => "Fri Dec 12"
s[0]?          # => "Fri Dec 12"
s[1]?          # => "Fri"
s[2]?          # => "Dec"
s[3]?          # => "12"
s[4]?          # => nil
s["wday"]?     # => "Fri"
s["month"]?    # => "Dec"
s["day"]?      # => "12"
s["year"]?     # => nil
s.scan(/more/) # => nil
s[0]?          # => nil

View source
def check(pattern) #

Returns the value that #scan would return, without advancing the scan offset. The last match is still saved, however.

s = StringScanner.new("this is a string")
s.offset = 5
s.check(/\w+/) # => "is"
s.check(/\w+/) # => "is"

View source
def check_until(pattern) #

Returns the value that #scan_until would return, without advancing the scan offset. The last match is still saved, however.

s = StringScanner.new("test string")
s.check_until(/tr/) # => "test str"
s.check_until(/g/)  # => "test string"

View source
def eos? #

Returns true if the scan offset is at the end of the string.

s = StringScanner.new("this is a string")
s.eos?                # => false
s.scan(/(\w+\s?){4}/) # => "this is a string"
s.eos?                # => true

View source
def inspect(io : IO) #

Writes a representation of the scanner.

Includes the current position of the offset, the total size of the string, and five characters near the current position.


View source
def offset #

Returns the current position of the scan offset.


View source
def offset=(position : Int) #

Sets the position of the scan offset.


View source
def peek(len) #

Extracts a string corresponding to string[offset,len], without advancing the scan offset.


View source
def reset #

Resets the scan offset to the beginning and clears the last match.


View source
def rest #

Returns the remainder of the string after the scan offset.

s = StringScanner.new("this is a string")
s.scan(/(\w+\s?){2}/) # => "this is "
s.rest                # => "a string"

View source
def scan(pattern) #

Tries to match with pattern at the current position. If there's a match, the scanner advances the scan offset, the last match is saved, and it returns the matched string. Otherwise, the scanner returns nil.

s = StringScanner.new("test string")
s.scan(/\w+/)   # => "test"
s.scan(/\w+/)   # => nil
s.scan(/\s\w+/) # => " string"
s.scan(/.*/)    # => nil

View source
def scan_until(pattern) #

Scans the string until the pattern is matched. Returns the substring up to and including the end of the match, the last match is saved, and advances the scan offset. Returns nil if no match.

s = StringScanner.new("test string")
s.scan_until(/tr/) # => "test str"
s.scan_until(/tr/) # => nil
s.scan_until(/g/)  # => "ing"

View source
def skip(pattern) #

Attempts to skip over the given pattern beginning with the scan offset. In other words, the pattern is not anchored to the current scan offset.

If there's a match, the scanner advances the scan offset, the last match is saved, and it returns the size of the skipped match. Otherwise it returns nil and does not advance the offset.

This method is the same as #scan, but without returning the matched string.


View source
def skip_until(pattern) #

Attempts to skip until the given pattern is found after the scan offset. In other words, the pattern is not anchored to the current scan offset.

If there's a match, the scanner advances the scan offset, the last match is saved, and it returns the size of the skip. Otherwise it returns nil and does not advance the offset.

This method is the same as #scan_until, but without returning the matched string.


View source
def string : String #

Returns the string being scanned.


View source
def terminate #

Moves the scan offset to the end of the string and clears the last match.


View source