strings/stringio_ungetc.rb

tests/_examples/strings/stringio_ungetc.rb in the metorex repository.

require "stringio"
require "strscan"

# Characters put back replace the bytes before the cursor, and what does not
# fit in front of it is added to the start.
io = StringIO.new(+"1234")
io.ungetc("A")
p io.string
io = StringIO.new(+"1234")
io.pos = 2
io.ungetc("φ")
p [io.pos, io.string]
io = StringIO.new(+"1234")
io.pos = 2
io.ungetc("foo")
p [io.pos, io.string]

# A character read and put back is read again whole.
io = StringIO.new(+"∂φ/")
io.ungetc(io.getc)
p io.readpartial(3).bytes.size
p io.read

# The rest a scanner has left is counted in bytes.
scanner = StringScanner.new("φx")
p scanner.rest_size

Output:

"A1234"
[0, "φ34"]
[0, "foo34"]
3
"φ/"
3