filesystem/reopened_streams_parens.rb

tests/_examples/filesystem/reopened_streams_parens.rb in the metorex repository.

# `IO#reopen` points a stream at another place without changing the object.
# Given a path it opens that file, and given another stream it takes both the
# descriptor and the class of that stream.
require "tmpdir"

first = File.join(Dir.tmpdir, "metorex_reopened_parens_first.txt")
second = File.join(Dir.tmpdir, "metorex_reopened_parens_second.txt")

File.write(first, "first line\n")
File.write(second, "second line\n")

reading = File.open(first, "r")
held = reading.object_id
p(reading.gets)
p(reading.reopen(second).equal?(reading))
p(reading.object_id == held)
p(reading.gets)
p(reading.path == second)
reading.close

# Written with no mode of its own, the file is opened the way the stream
# already was, so one opened for writing makes the file.
writing = File.open(first, "w")
writing.reopen(second)
writing.print("written through")
writing.close
p(File.read(second))

# Pointed at another stream, the object takes that stream's class.
File.write(first, "back again\n")
plain = IO.new(IO.sysopen(first, "r"), "r")
named = File.open(second, "r")
p(named.class)
p(named.reopen(plain).class)
p(named.gets)
named.close
plain.close

# A stream pointed somewhere else is open again even when it was closed.
closed = File.open(first, "r")
closed.close
p(closed.closed?)
closed.reopen(second)
p(closed.closed?)
p(closed.close_on_exec?)
closed.close

File.delete(first)
File.delete(second)

Output:

"first line\n"
true
true
"second line\n"
true
"written through"
File
IO
"back again\n"
true
false
true