regcomp.c: Make comment more accurate

[perl5.git] / lib / PerlIO.pm

diff --git a/lib/PerlIO.pm b/lib/PerlIO.pm
index c0acdec..c94685b 100644 (file)
--- a/lib/PerlIO.pm
+++ b/lib/PerlIO.pm
@@ -1,6 +1,6 @@
 package PerlIO;
 
 package PerlIO;
 

-our $VERSION = '1.04';
+our $VERSION = '1.07';

 
 # Map layer name to package that defines it
 our %alias;
 
 # Map layer name to package that defines it
 our %alias;


@@ -71,7 +71,7 @@ UNIX/POSIX numeric file descriptor calls
 
 Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc.  Note
 that as this is "real" stdio it will ignore any layers beneath it and
 
 Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc.  Note
 that as this is "real" stdio it will ignore any layers beneath it and

-got straight to the operating system via the C library as usual.
+go straight to the operating system via the C library as usual.

 
 =item :perlio
 
 
 =item :perlio
 


@@ -85,40 +85,14 @@ C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
 
 A layer that implements DOS/Windows like CRLF line endings.  On read
 converts pairs of CR,LF to a single "\n" newline character.  On write
 
 A layer that implements DOS/Windows like CRLF line endings.  On read
 converts pairs of CR,LF to a single "\n" newline character.  On write

-converts each "\n" to a CR,LF pair.  Note that this layer likes to be
-one of its kind: it silently ignores attempts to be pushed into the
-layer stack more than once.
+converts each "\n" to a CR,LF pair.  Note that this layer will silently
+refuse to be pushed on top of itself.

 
 It currently does I<not> mimic MS-DOS as far as treating of Control-Z
 as being an end-of-file marker.
 
 
 It currently does I<not> mimic MS-DOS as far as treating of Control-Z
 as being an end-of-file marker.
 

-(Gory details follow) To be more exact what happens is this: after
-pushing itself to the stack, the C<:crlf> layer checks all the layers
-below itself to find the first layer that is capable of being a CRLF
-layer but is not yet enabled to be a CRLF layer.  If it finds such a
-layer, it enables the CRLFness of that other deeper layer, and then
-pops itself off the stack.  If not, fine, use the one we just pushed.
-
-The end result is that a C<:crlf> means "please enable the first CRLF
-layer you can find, and if you can't find one, here would be a good
-spot to place a new one."
-

 Based on the C<:perlio> layer.
 
 Based on the C<:perlio> layer.
 

-=item :mmap
-
-A layer which implements "reading" of files by using C<mmap()> to
-make (whole) file appear in the process's address space, and then
-using that as PerlIO's "buffer". This I<may> be faster in certain
-circumstances for large files, and may result in less physical memory
-use when multiple processes are reading the same file.
-
-Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
-layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
-needs extra house-keeping (to extend the file) which negates any advantage.
-
-The C<:mmap> layer will not exist if platform does not support C<mmap()>.
-

 =item :utf8
 
 Declares that the stream accepts perl's I<internal> encoding of
 =item :utf8
 
 Declares that the stream accepts perl's I<internal> encoding of


@@ -139,35 +113,39 @@ and then read it back in.
        $in = <F>;
        close(F);
 
        $in = <F>;
        close(F);
 

+Note that this layer does not validate byte sequences. For reading
+input, using C<:encoding(utf8)> instead of bare C<:utf8> is strongly
+recommended.
+

 =item :bytes
 
 =item :bytes
 

-This is the inverse of C<:utf8> layer. It turns off the flag
+This is the inverse of the C<:utf8> layer. It turns off the flag

 on the layer below so that data read from it is considered to
 on the layer below so that data read from it is considered to

-be "octets" i.e. characters in range 0..255 only. Likewise
+be "octets" i.e. characters in the range 0..255 only. Likewise

 on output perl will warn if a "wide" character is written
 to a such a stream.
 
 =item :raw
 
 The C<:raw> layer is I<defined> as being identical to calling
 on output perl will warn if a "wide" character is written
 to a such a stream.
 
 =item :raw
 
 The C<:raw> layer is I<defined> as being identical to calling

-C<binmode($fh)> - the stream is made suitable for passing binary data
+C<binmode($fh)> - the stream is made suitable for passing binary data,

 i.e. each byte is passed as-is. The stream will still be
 buffered.
 
 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
 referred to as a "discipline") is documented as the inverse of the
 C<:crlf> layer. That is no longer the case - other layers which would
 i.e. each byte is passed as-is. The stream will still be
 buffered.
 
 In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
 referred to as a "discipline") is documented as the inverse of the
 C<:crlf> layer. That is no longer the case - other layers which would

-alter binary nature of the stream are also disabled.  If you want UNIX
+alter the binary nature of the stream are also disabled.  If you want UNIX

 line endings on a platform that normally does CRLF translation, but still
 line endings on a platform that normally does CRLF translation, but still

-want UTF-8 or encoding defaults the appropriate thing to do is to add
-C<:perlio> to PERLIO environment variable.
+want UTF-8 or encoding defaults, the appropriate thing to do is to add
+C<:perlio> to the PERLIO environment variable.

 
 The implementation of C<:raw> is as a pseudo-layer which when "pushed"
 pops itself and then any layers which do not declare themselves as suitable
 for binary data. (Undoing :utf8 and :crlf are implemented by clearing
 flags rather than popping layers but that is an implementation detail.)
 
 
 The implementation of C<:raw> is as a pseudo-layer which when "pushed"
 pops itself and then any layers which do not declare themselves as suitable
 for binary data. (Undoing :utf8 and :crlf are implemented by clearing
 flags rather than popping layers but that is an implementation detail.)
 

-As a consequence of the fact that C<:raw> normally pops layers
+As a consequence of the fact that C<:raw> normally pops layers,

 it usually only makes sense to have it as the only or first element in
 a layer specification.  When used as the first element it provides
 a known base on which to build e.g.
 it usually only makes sense to have it as the only or first element in
 a layer specification.  When used as the first element it provides
 a known base on which to build e.g.


@@ -194,8 +172,8 @@ A more elegant (and safer) interface is needed.
 
 =item :win32
 
 
 =item :win32
 

-On Win32 platforms this I<experimental> layer uses native "handle" IO
-rather than unix-like numeric file descriptor layer. Known to be
+On Win32 platforms this I<experimental> layer uses the native "handle" IO
+rather than the unix-like numeric file descriptor layer. Known to be

 buggy as of perl 5.8.2.
 
 =back
 buggy as of perl 5.8.2.
 
 =back


@@ -211,11 +189,25 @@ in Perl using the latter) come with the Perl distribution.
 =item :encoding
 
 Use C<:encoding(ENCODING)> either in open() or binmode() to install
 =item :encoding
 
 Use C<:encoding(ENCODING)> either in open() or binmode() to install

-a layer that does transparently character set and encoding transformations,
+a layer that transparently does character set and encoding transformations,

 for example from Shift-JIS to Unicode.  Note that under C<stdio>
 an C<:encoding> also enables C<:utf8>.  See L<PerlIO::encoding>
 for more information.
 
 for example from Shift-JIS to Unicode.  Note that under C<stdio>
 an C<:encoding> also enables C<:utf8>.  See L<PerlIO::encoding>
 for more information.
 

+=item :mmap
+
+A layer which implements "reading" of files by using C<mmap()> to
+make a (whole) file appear in the process's address space, and then
+using that as PerlIO's "buffer". This I<may> be faster in certain
+circumstances for large files, and may result in less physical memory
+use when multiple processes are reading the same file.
+
+Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
+layer. Writes also behave like the C<:perlio> layer, as C<mmap()> for write
+needs extra house-keeping (to extend the file) which negates any advantage.
+
+The C<:mmap> layer will not exist if the platform does not support C<mmap()>.
+

 =item :via
 
 Use C<:via(MODULE)> either in open() or binmode() to install a layer
 =item :via
 
 Use C<:via(MODULE)> either in open() or binmode() to install a layer


@@ -232,10 +224,10 @@ To get a binary stream an alternate method is to use:
     open($fh,"whatever")
     binmode($fh);
 
     open($fh,"whatever")
     binmode($fh);
 

-this has advantage of being backward compatible with how such things have
+this has the advantage of being backward compatible with how such things have

 had to be coded on some platforms for years.
 
 had to be coded on some platforms for years.
 

-To get an un-buffered stream specify an unbuffered layer (e.g. C<:unix>)
+To get an unbuffered stream specify an unbuffered layer (e.g. C<:unix>)

 in the open call:
 
     open($fh,"<:unix",$path)
 in the open call:
 
     open($fh,"<:unix",$path)


@@ -250,7 +242,7 @@ translation for text files then the default layers are :
 (The low level "unix" layer may be replaced by a platform specific low
 level layer.)
 
 (The low level "unix" layer may be replaced by a platform specific low
 level layer.)
 

-Otherwise if C<Configure> found out how to do "fast" IO using system's
+Otherwise if C<Configure> found out how to do "fast" IO using the system's

 stdio, then the default layers are:
 
   unix stdio
 stdio, then the default layers are:
 
   unix stdio


@@ -271,7 +263,7 @@ This can be used to see the effect of/bugs in the various layers e.g.
   PERLIO=stdio  ./perl harness
   PERLIO=perlio ./perl harness
 
   PERLIO=stdio  ./perl harness
   PERLIO=perlio ./perl harness
 

-For the various value of PERLIO see L<perlrun/PERLIO>.
+For the various values of PERLIO see L<perlrun/PERLIO>.

 
 =head2 Querying the layers of filehandles
 
 
 =head2 Querying the layers of filehandles
 


@@ -285,20 +277,19 @@ system and on the Perl version, and both the compile-time and
 runtime configurations of Perl.
 
 The following table summarizes the default layers on UNIX-like and
 runtime configurations of Perl.
 
 The following table summarizes the default layers on UNIX-like and

-DOS-like platforms and depending on the setting of the C<$ENV{PERLIO}>:
+DOS-like platforms and depending on the setting of C<$ENV{PERLIO}>:

 
  PERLIO     UNIX-like                   DOS-like
  ------     ---------                   --------
  unset / "" unix perlio / stdio [1]     unix crlf
  stdio      unix perlio / stdio [1]     stdio
  perlio     unix perlio                 unix perlio
 
  PERLIO     UNIX-like                   DOS-like
  ------     ---------                   --------
  unset / "" unix perlio / stdio [1]     unix crlf
  stdio      unix perlio / stdio [1]     stdio
  perlio     unix perlio                 unix perlio

- mmap       unix mmap                   unix mmap

 
  # [1] "stdio" if Configure found out how to do "fast stdio" (depends
  # on the stdio implementation) and in Perl 5.8, otherwise "unix perlio"
 
 
  # [1] "stdio" if Configure found out how to do "fast stdio" (depends
  # on the stdio implementation) and in Perl 5.8, otherwise "unix perlio"
 

-By default the layers from the input side of the filehandle is
-returned, to get the output side use the optional C<output> argument:
+By default the layers from the input side of the filehandle are
+returned; to get the output side, use the optional C<output> argument:

 
    my @layers = PerlIO::get_layers($fh, output => 1);
 
 
    my @layers = PerlIO::get_layers($fh, output => 1);
 


@@ -314,10 +305,10 @@ You are supposed to use open() and binmode() to manipulate the stack.
 
 B<Implementation details follow, please close your eyes.>
 
 
 B<Implementation details follow, please close your eyes.>
 

-The arguments to layers are by default returned in parenthesis after
+The arguments to layers are by default returned in parentheses after

 the name of the layer, and certain layers (like C<utf8>) are not real
 the name of the layer, and certain layers (like C<utf8>) are not real

-layers but instead flags on real layers: to get all of these returned
-separately use the optional C<details> argument:
+layers but instead flags on real layers; to get all of these returned
+separately, use the optional C<details> argument:

 
    my @layer_and_args_and_flags = PerlIO::get_layers($fh, details => 1);
 
 
    my @layer_and_args_and_flags = PerlIO::get_layers($fh, details => 1);