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digitalmars.D.bugs - [Issue 3057] New: Add pure annotations to core.stdc.*

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3057

           Summary: Add pure annotations to core.stdc.*
           Product: D
           Version: 2.030
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: patch
          Severity: enhancement
          Priority: P2
         Component: druntime
        AssignedTo: sean invisibleduck.org
        ReportedBy: braddr puremagic.com


Created an attachment (id=395)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=395)
Add pure annotations throughout std.core.*

I did a quick pass through core.stdc.* to annotate the functions I believe
should be pure.  I added some comments for several that could be stretched to
be pure if we're a little looser with the definition of pure.  I skipped over
the floating point areas as there's been a good amount of debate that I haven't
followed over what to do with them.  I defer to Don and Walter on those.

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Jun 07 2009
next sibling parent d-bugmail puremagic.com writes:
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PDT ---
(From update of attachment 395)
note: I varied the style used to annotate some parts to get a feel for how they
looked.  A second pass should be done to choose a common style.

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PDT ---
Created an attachment (id=397)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=397)
same set of changes with pure as after the declaration annotation

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au







 Created an attachment (id=395)


 --> (http://d.puremagic.com/issues/attachment.cgi?id=395) [details]

 Add pure annotations throughout std.core.*
 
 I did a quick pass through core.stdc.* to annotate the functions I believe
 should be pure.  I added some comments for several that could be stretched to
 be pure if we're a little looser with the definition of pure.  I skipped over
 the floating point areas as there's been a good amount of debate that I haven't
 followed over what to do with them.  I defer to Don and Walter on those.


Almost all functions in stdc.math cannot possibly be pure, because they set the
global 'errno'. (This is part of the reason why it has been worthwhile to
re-implement most C math functions in D). There are a few functions (like
fpclassify() and the trivial functions which use it) which _could_ legally be
marked as pure, but I really don't think that use of stdc.math should be
encouraged in any way in D code. So the math stuff is not a TODO list thing, it
should stay as impure.

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Jun 08 2009
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PDT ---
Don,
  Works for me.. core.stdc.math stays impure.  I'll put your response in there
as a comment to help prevent re-addressing this issue.

  How about core.stdc.complex?  A quick scan of some of the man pages suggest
that they don't touch errno.

----

Sean,
  Any thoughts on the several I added comments to, like all the ones that use
the external LC_CTYPE??

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Jun 08 2009
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PDT ---
I'd consider environment variables to be global state, and so no function using
them could be pure.  As for some of the ones you'd specifically marked,
strftime() uses the LC_TIME category of the current locale, which is global
mutable state as well.

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Jun 09 2009
prev sibling next sibling parent d-bugmail puremagic.com writes:
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PDT ---
String functions are also impure because their arguments can be mutable.

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PDT ---


 String functions are also impure because their arguments can be mutable.


Please be specific.  The string functions I marked pure in the attached diffs
should be fine.  They're taking const non-shared char pointers, which is safe.

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PDT ---
char* str1=obj.str1;
const char* str2=obj.str2;
auto len1=strlen(str2);
str1[0]=0;
auto len2=strlen(str2);
assert(str1==str2,"pwnd");

GCC has stricter definition of pure function - a function whose arguments are
contained in the stack (no reference types), in D this definition is extended
to include immutable reference types, because they effectively behave as value
types.

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Jun 11 2009
prev sibling next sibling parent d-bugmail puremagic.com writes:
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PDT ---
assert(str1!=str2,"pwnd");

*fixed

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PDT ---


 char* str1=obj.str1;
 const char* str2=obj.str2;
 auto len1=strlen(str2);
 str1[0]=0;
 auto len2=strlen(str2);
 assert(str1!=str2,"pwnd");
 
 GCC has stricter definition of pure function - a function whose arguments are
 contained in the stack (no reference types), in D this definition is extended
 to include immutable reference types, because they effectively behave as value
 types.


That's fine.  That's not a violation of purity as D has defined it.  Purity is
defined, roughly, as:

  1) does not mutate global state
  2) does not depend on global state

or:
  Depends only on it's inputs and mutates only its output.

strlen is a classic example of a pure function.

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PDT ---
Reference type is an example of global state in the sense that it can change
unexpectedly. Dependency on global state is impure because it prevents
reordering of function calls and caching function results. My example
demonstrates, why strlen calls can't be reordered or cached, which proves its
impurity.

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Jun 23 2009
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PDT ---
strlen is a classic example of a pure function because classic strings are
immutable which is not the case for C strings and strlen.

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Jun 23 2009
prev sibling parent d-bugmail puremagic.com writes:
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Alex Rønne Petersen <alex lycus.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |alex lycus.org
         Resolution|                            |FIXED



CEST ---
I sent a pull request a while back that added safety, purity, and nothrow
annotations throughout core.stdc (not having noticed the patch here). I'll
close this, but if it turns out I forgot some annotations, please reopen.

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Oct 09 2012