Hi,
I suggest to add a method readn to the IO class (and to StringIO,
Socket...), which behaves similar to read(n), but raises an exception if
the returned string is not of size n.
class IO
def readn(n)
str = read(n)
raise if str.nil? or str.size != n
str
end
end
It's annoying to test for it in the application.
Regards,
Michael
don't you think the code will be just as long/annoying with a begin/rescue
block?
-a
On Sun, 20 Jun 2004, Michael Neumann wrote:
Hi,
I suggest to add a method readn to the IO class (and to StringIO,
Socket...), which behaves similar to read(n), but raises an exception if
the returned string is not of size n.class IO
def readn(n)
str = read(n)
raise if str.nil? or str.size != n
str
end
endIt's annoying to test for it in the application.
Regards,
Michael
EMAIL :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
PHONE :: 303.497.6469
A flower falls, even though we love it; and a weed grows, even though we do
not love it. --Dogen
===============================================================================
Michael Neumann wrote:
Hi,
I suggest to add a method readn to the IO class (and to StringIO,
Socket...), which behaves similar to read(n), but raises an exception if
the returned string is not of size n.class IO
def readn(n)
str = read(n)
raise if str.nil? or str.size != n
str
end
end
Here's an option that gives the programmer the option of chosing whether to to use "at most" or "exactly" semantics. As bonus, it also allows "at least" and "0 or N, but nothing in between" semantics.
Also, since it doesn't accept a Fixnum argument, it forces the programmer to be clear about the chosen semantics.
----
module ReadExt
def read_inclusive(enum = nil)
str = read(enum && enum.max)
str_size = str ? str.size : 0
if enum and not enum.include?(str_size)
raise RangeError
end
str
end
end
require 'stringio'
class IO; include ReadExt; end
class StringIO; include ReadExt; end
io = StringIO.new
io.write(('a'..'z').to_a)
io.rewind
p io.read_inclusive(20..30) # ==> "abcdefghijklmnopqrstuvwxyz"
p io.read_inclusive # ==> ""
begin
p io.read_inclusive(5..5)
rescue RangeError
puts "nothing left to read" # ==> nothing left to read
end
io.rewind
p io.read_inclusive(0..10) # ==> "abcdefghij"
io.rewind
p io.read_inclusive(20..20) # ==> "abcdefghijklmnopqrst"
begin
io.rewind
p io.read_inclusive(30..30)
rescue RangeError
puts "alphabet underflow" # ==> alphabet underflow
end
io.rewind
p io.read_inclusive # ==> "abcdefghijklmnopqrstuvwxyz"
p io.read_inclusive(0..100) # ==> nil
io.rewind
3.times do
# automatically checks for "complete" blocks of 13
p io.read_inclusive([0,13])
# ==> "abcdefghijklm"
# ==> "nopqrstuvwxyz"
# ==> nil
end
No, as I wouldn't use a rescue clause in this case. It's better to crash
early than proceed with a wrong value.
I never liked it that read(4) might return only 3 characters.
Regards,
Michael
On Sun, Jun 20, 2004 at 01:33:18AM +0900, Ara.T.Howard wrote:
On Sun, 20 Jun 2004, Michael Neumann wrote:
>Hi,
>
>I suggest to add a method readn to the IO class (and to StringIO,
>Socket...), which behaves similar to read(n), but raises an exception if
>the returned string is not of size n.
>
> class IO
> def readn(n)
> str = read(n)
> raise if str.nil? or str.size != n
> str
> end
> end
>
>It's annoying to test for it in the application.
>
>Regards,
>
> Michaeldon't you think the code will be just as long/annoying with a begin/rescue
block?
[snip]
I never liked it that read(4) might return only 3 characters.
Wouldn't it be better then to change the behavier of #read itself, so
it fails per default in case the specified number of bytes cannot be read.
with ruby2 we should try to break as much as possible, and hopefully
get it right.
#readn smells too much like workaround 
On Saturday 19 June 2004 19:01, Michael Neumann wrote:
--
Simon Strandgaard
but another read may give one more byte - then you'd have your 4? even if one
implemented IO#read(n) i'd think you'd want:
class IO
def readn n
buf = ''
buf << read(n - buf.size) until buf.size == n
buf
end
end
which give you what you want (n bytes), or throws EOFError.
-a
On Sun, 20 Jun 2004, Michael Neumann wrote:
On Sun, Jun 20, 2004 at 01:33:18AM +0900, Ara.T.Howard wrote:
On Sun, 20 Jun 2004, Michael Neumann wrote:
Hi,
I suggest to add a method readn to the IO class (and to StringIO,
Socket...), which behaves similar to read(n), but raises an exception if
the returned string is not of size n.class IO
def readn(n)
str = read(n)
raise if str.nil? or str.size != n
str
end
endIt's annoying to test for it in the application.
Regards,
Michael
don't you think the code will be just as long/annoying with a begin/rescue
block?No, as I wouldn't use a rescue clause in this case. It's better to crash
early than proceed with a wrong value.I never liked it that read(4) might return only 3 characters.
Regards,
Michael
EMAIL :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
PHONE :: 303.497.6469
A flower falls, even though we love it; and a weed grows, even though we do
not love it. --Dogen
===============================================================================
Right. You have my vote for it!
But I fear, as #read resembles the UNIX read(2) syscall, this change
will not happen in Ruby2.
Regards,
Michael
On Sun, Jun 20, 2004 at 02:07:51AM +0900, Simon Strandgaard wrote:
On Saturday 19 June 2004 19:01, Michael Neumann wrote:
[snip]
>
> I never liked it that read(4) might return only 3 characters.
>Wouldn't it be better then to change the behavier of #read itself, so
it fails per default in case the specified number of bytes cannot be read.with ruby2 we should try to break as much as possible, and hopefully
get it right.
I agree, a method called to read n bytes should raise an exception when it
cannot.
Sean O'Dell
On Saturday 19 June 2004 10:07, Simon Strandgaard wrote:
On Saturday 19 June 2004 19:01, Michael Neumann wrote:
[snip]> I never liked it that read(4) might return only 3 characters.
Wouldn't it be better then to change the behavier of #read itself, so
it fails per default in case the specified number of bytes cannot be read.with ruby2 we should try to break as much as possible, and hopefully
get it right.#readn smells too much like workaround
[...]
I agree, a method called to read n bytes should raise an exception when it
cannot.
Except that the semantics of read() specify that _at most_ n bytes will
be read. There are important cases where you want these semantics, such
as when reading from a non-blocking socket or pipe or when reading a
file in chunks without wanting to bother to find out what exactly the
size of the last chunk will be (which can be impossible if the file is
not seekable).
Reimer Behrends
Sean O'Dell (sean@celsoft.com) wrote:
Yep, you're right...I guess that would apply even in a scripted environment.
Sean O'Dell
On Saturday 19 June 2004 11:58, Reimer Behrends wrote:
Sean O'Dell (sean@celsoft.com) wrote:
[...]> I agree, a method called to read n bytes should raise an exception when
> it cannot.Except that the semantics of read() specify that _at most_ n bytes will
be read. There are important cases where you want these semantics, such
as when reading from a non-blocking socket or pipe or when reading a
file in chunks without wanting to bother to find out what exactly the
size of the last chunk will be (which can be impossible if the file is
not seekable).
exactly. if don't like the way it works now, try writing code which reads
from network socket using a read(n) which throws exceptions. THAT will be
ugly...
-a
On Sat, 19 Jun 2004, Reimer Behrends wrote:
Sean O'Dell (sean@celsoft.com) wrote:
[...]I agree, a method called to read n bytes should raise an exception when it
cannot.Except that the semantics of read() specify that _at most_ n bytes will
be read. There are important cases where you want these semantics, such
as when reading from a non-blocking socket or pipe or when reading a
file in chunks without wanting to bother to find out what exactly the
size of the last chunk will be (which can be impossible if the file is
not seekable).Reimer Behrends
EMAIL :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
PHONE :: 303.497.6469
A flower falls, even though we love it; and a weed grows, even though we do
not love it. --Dogen
===============================================================================