instance method

StringScanner#unscan

() -> void

unscan → self

static VALUE
strscan_unscan(VALUE self)
{
    struct strscanner *p;

    GET_SCANNER(self, p);
    if (! MATCHED_P(p))
        rb_raise(ScanError, "unscan failed: previous match record not exist");
    p->curr = p->prev;
    CLEAR_MATCH_STATUS(p);
    return self;
}

Sets the position to its value previous to the recent successful match attempt:

Example

scanner = StringScanner.new('foobarbaz')
scanner.scan(/foo/)
put_situation(scanner)
# Situation:
#   pos:       3
#   charpos:   3
#   rest:      "barbaz"
#   rest_size: 6
scanner.unscan
# => #<StringScanner 0/9 @ "fooba...">
put_situation(scanner)
# Situation:
#   pos:       0
#   charpos:   0
#   rest:      "foobarbaz"
#   rest_size: 9

Raises an exception if match values are clear:

Example

scanner.scan(/nope/)           # => nil
match_values_cleared?(scanner) # => true
scanner.unscan                 # Raises StringScanner::Error.

See also #terminate #values_at #string= also in 4.1 · 3.4 · 3.3 · 3.2 · 3.1 · 3.0

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