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Re: RAII vs gc (was fortran lib which provide python like data type)

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From Devin Jeanpierre <jeanpierreda@gmail.com>
Date Sat, 31 Jan 2015 19:27:22 -0800
Subject Re: RAII vs gc (was fortran lib which provide python like data type)
To Sturla Molden <sturla.molden@gmail.com>
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On Fri, Jan 30, 2015 at 1:28 PM, Sturla Molden <sturla.molden@gmail.com> wrote:
> in Python. It actually corresponds to
>
> with Foo() as bar:
>     <suite>

The problem with with statements is that they only handle the case of
RAII with stack allocated variables, and can't handle transfer of
ownership cleanly.

Consider the case of a function that opens a file and returns it:

def myfunction(name, stuff):
    f = open(name)
    f.seek(stuff) # or whatever
    return f

def blahblah():
    with myfunction('hello', 12) as f:
         ....

This code is wrong, because if an error occurs during seek in
myfunction, the file is leaked.

The correct myfunction is as follows:

def myfunction(name, stuff)
    f = open(name)
    try:
        f.seek(stuff)
    except:
        f.close()
        raise

Or whatever. (I would love a close_on_error context manager, BTW.)

With RAII, the equivalent C++ looks nearly exactly like the original
(bad) Python approach, except it uses unique_ptr to store the file,
and isn't broken. ("Modern") C++ makes this easy to get right. But
then, this isn't the common case.

-- Devin

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[OT] fortran lib which provide python like data type 1989lzhh <1989lzhh@gmail.com> - 2015-01-29 21:39 +0800
  Re: [OT] fortran lib which provide python like data type beliavsky@aol.com - 2015-01-29 14:39 -0800
    Re: [OT] fortran lib which provide python like data type Rustom Mody <rustompmody@gmail.com> - 2015-01-29 17:40 -0800
      Re: [OT] fortran lib which provide python like data type Christian Gollwitzer <auriocus@gmx.de> - 2015-01-30 08:32 +0100
        Re: [OT] fortran lib which provide python like data type Rustom Mody <rustompmody@gmail.com> - 2015-01-30 08:27 -0800
          Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-01-30 10:08 -0700
            Re: [OT] fortran lib which provide python like data type Rustom Mody <rustompmody@gmail.com> - 2015-01-30 09:31 -0800
              RAII vs gc (was fortran lib which provide python like data type) Rustom Mody <rustompmody@gmail.com> - 2015-01-30 10:02 -0800
                Re: RAII vs gc (was fortran lib which provide python like data type) Sturla Molden <sturla.molden@gmail.com> - 2015-01-30 21:28 +0000
                Re: RAII vs gc (was fortran lib which provide python like data type) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-01 14:00 +1100
                Re: RAII vs gc (was fortran lib which provide python like data type) Chris Angelico <rosuav@gmail.com> - 2015-02-01 14:21 +1100
                Re: RAII vs gc (was fortran lib which provide python like data type) Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-01-31 19:27 -0800
              Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-01-30 11:15 -0700
                Re: [OT] fortran lib which provide python like data type Paul Rubin <no.email@nospam.invalid> - 2015-01-30 10:23 -0800
                Re: [OT] fortran lib which provide python like data type Christian Gollwitzer <auriocus@gmx.de> - 2015-01-31 09:27 +0100
                Re: [OT] fortran lib which provide python like data type Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-31 11:51 +1300
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-31 10:49 +1100
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-01-31 14:22 +0200
                Re: [OT] fortran lib which provide python like data type Rustom Mody <rustompmody@gmail.com> - 2015-01-31 07:50 -0800
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-01-31 19:43 +0200
                Re: [OT] fortran lib which provide python like data type Rustom Mody <rustompmody@gmail.com> - 2015-01-31 18:30 -0800
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-01 09:38 +0200
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-02 03:49 +1100
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-01 20:57 +0200
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-02 12:59 +1100
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-02 13:05 +1100
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-02 10:51 +0200
                Re: [OT] fortran lib which provide python like data type Chris Angelico <rosuav@gmail.com> - 2015-02-02 13:04 +1100
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-02 18:01 +1100
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-02 10:52 +0200
                Re: [OT] fortran lib which provide python like data type Paul Rudin <paul.nospam@rudin.co.uk> - 2015-02-02 12:56 +0000
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-02 15:27 +0200
                Re: [OT] fortran lib which provide python like data type Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-02 16:08 +0000
                Re: [OT] fortran lib which provide python like data type Rustom Mody <rustompmody@gmail.com> - 2015-02-02 08:21 -0800
                Re: [OT] fortran lib which provide python like data type Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-02 16:52 +0000
                Re: [OT] fortran lib which provide python like data type Chris Angelico <rosuav@gmail.com> - 2015-02-03 04:25 +1100
                Re: [OT] fortran lib which provide python like data type Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-02 18:34 +0000
                Re: [OT] fortran lib which provide python like data type Chris Angelico <rosuav@gmail.com> - 2015-02-03 10:15 +1100
                Re: [OT] fortran lib which provide python like data type Matthew Barnett <auxlang@mrabarnett.plus.com> - 2015-02-02 02:35 +0000
                Re: [OT] fortran lib which provide python like data type Chris Angelico <rosuav@gmail.com> - 2015-02-02 13:45 +1100
                Re: [OT] fortran lib which provide python like data type Roy Smith <roy@panix.com> - 2015-02-01 23:12 -0500
                Re: [OT] fortran lib which provide python like data type Roy Smith <roy@panix.com> - 2015-02-01 23:14 -0500
                Re: [OT] fortran lib which provide python like data type Chris Angelico <rosuav@gmail.com> - 2015-02-02 15:47 +1100
                Re: [OT] fortran lib which provide python like data type Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-02 16:06 +0000
                Re: [OT] fortran lib which provide python like data type Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-01-31 17:59 +0000
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-01 13:27 +1100
                Re: [OT] fortran lib which provide python like data type Paul Rubin <no.email@nospam.invalid> - 2015-01-31 22:26 -0800
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-01 09:58 +0200
                Re: [OT] fortran lib which provide python like data type Christian Gollwitzer <auriocus@gmx.de> - 2015-02-01 09:14 +0100
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-01 21:12 +0200
                Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-02-01 17:50 -0700
                Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-02-01 18:02 -0700
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-02 09:39 +0200
                Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-02-02 09:25 -0700
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-02 19:57 +0200
                Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-02-02 11:23 -0700
                Re: [OT] fortran lib which provide python like data type Marko Rauhamaa <marko@pacujo.net> - 2015-02-02 20:54 +0200
                Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-02-01 18:02 -0700
                Re: [OT] fortran lib which provide python like data type beliavsky@aol.com - 2015-02-02 05:30 -0800
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-31 10:50 +1100
                Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-01-30 20:49 -0700
                Re: [OT] fortran lib which provide python like data type Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-31 22:04 +1100
                Re: [OT] fortran lib which provide python like data type Rustom Mody <rustompmody@gmail.com> - 2015-01-31 08:18 -0800
          Re: [OT] fortran lib which provide python like data type Sturla Molden <sturla.molden@gmail.com> - 2015-01-30 23:12 +0000
          Re: [OT] fortran lib which provide python like data type Michael Torrie <torriem@gmail.com> - 2015-01-30 20:35 -0700

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