filesystem/opening_modes_parens.rb

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

# A mode string is `r`, `w` or `a`, then any of `+`, `b` or `t` but not both
# of the last two, and `x` only after `w`. Anything else is refused.
path = "/tmp/metorex_opening_modes_#{Process.pid()}.txt"
File.write(path, "hello file\n")

def refusal()
  yield()
rescue StandardError => problem
  [problem.class(), problem.message()]
end

p(refusal() { File.open(path, "q") })
p(refusal() { File.open(path, "rbt") })
p(refusal() { File.open(path, "rx") })
p(refusal() { File.open(path, "rb", newline: :universal) })

# `x` asks for a file of its own.
p(refusal() { File.open(path, "wx") }[0])

# A numeric mode says for itself whether the file is written and cut down.
File.open(path, File::WRONLY) { |file| p(refusal() { file.gets() }) }
p(File.read(path))
File.open(path, File::TRUNC) { |file| p(file.gets()) }
p(File.size(path))
p(refusal() { File.open("#{path}.missing", File::WRONLY) }[0])

# A nil mode reads, and `b` in the mode puts the stream in binary mode.
File.open(path, nil, nil) { |file| p(file.class()) }
File.write(path, "testing\n")
File.open(path, "rb+") { |file| p([file.binmode?(), file.external_encoding(), file.pos()]) }

# With a block the file is closed through `close` after the block, and what
# that `close` raises is raised, except for a stream already closed.
closes = []
File.open(path) do |file|
  file.define_singleton_method(:close) do
    super()
    closes << :closed
    raise(StandardError, "from close")
  end
end rescue closes << $!.message()
p(closes)

File.delete(path)

Output:

[ArgumentError, "invalid access mode q"]
[ArgumentError, "invalid access mode rbt"]
[ArgumentError, "invalid access mode rx"]
[ArgumentError, "newline decorator with binary mode"]
Errno::EEXIST
[IOError, "not opened for reading"]
"hello file\n"
nil
0
Errno::ENOENT
File
[true, #<Encoding:BINARY (ASCII-8BIT)>, 0]
[:closed, "from close"]