December 11, 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8408



--- Comment #9 from bearophile_hugs@eml.cc 2012-12-10 18:31:16 PST ---
(In reply to comment #8)

> I'm not sure that this should be allowed.
> foo1 can rewrite the elements referred from arr, then it is deduced to weak
> purity. In current principle, the returned value from weak purity function
> cannot be converted to immutable implicitly (it is only allowed for strong
> purity function).
> 
> If you change the signature of foo1 to:
> 
>   char[] foo1(const int[] arr) pure;
> 
> Then foo1 will be deduced to strong purity, and implicit conversion to immutable for initializing x1 will be succeeded.

You are right, thank you for your answer.

(If you want me/us to try to suggest improvements in how you write in English, I am willing to help you, despite I am not a good English teacher.)

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December 11, 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8408


timon.gehr@gmx.ch changed:

           What    |Removed                     |Added
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--- Comment #10 from timon.gehr@gmx.ch 2012-12-10 18:37:41 PST ---
(In reply to comment #8)
> (In reply to comment #6)
> > Is it correct that x1 refused and x2 accepted?
> > 
> > 
> > char[] foo1(int[] arr) pure {
> >     return new char[10];
> > }
> > immutable(char)[] foo2(int[] arr) pure {
> >     return new char[10];
> > }
> > void main(string[] args) {
> >     immutable x1 = foo1([1, 2]); // Error: cannot implicitly convert
> >     immutable x2 = foo2([1, 2]); // OK
> > }
> 
> I'm not sure that this should be allowed.
> ...

Why not? It is known at the call site that anything foo1 will return is newly allocated. Strong or weak purity is irrelevant.

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December 11, 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8408



--- Comment #11 from Kenji Hara <k.hara.pg@gmail.com> 2012-12-10 19:39:00 PST ---
(In reply to comment #10)
> (In reply to comment #8)
> > (In reply to comment #6)
> > I'm not sure that this should be allowed.
> > ...
> 
> Why not? It is known at the call site that anything foo1 will return is newly allocated. Strong or weak purity is irrelevant.

Your argument had be true.

I had re-read issue 5081, and could be believed that between the purity level (strong, constant, weak) and the conversion possibility to immutable of returned value are irrelevant.

From: http://d.puremagic.com/issues/show_bug.cgi?id=5081#c2
> Note actually that as long as you can verify the return value did not come directly from the parameters, it's also possible to implicitly cast to immutable.
> 
> For example:
> 
> pure T[] mydup(T)(const(T)[] param) {...}
> 
> It's provable that the return value did not come from param (without a cast), because you can't implicitly cast param to T[].  So you can cast the result to immutable, >>>>even if param began as mutable<<<<.

The last sentence describes the ideal behavior.
Thanks a lot!

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January 16, 2013
http://d.puremagic.com/issues/show_bug.cgi?id=8408



--- Comment #12 from yebblies <yebblies@gmail.com> 2013-01-17 01:07:31 EST ---
*** Issue 6783 has been marked as a duplicate of this issue. ***

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http://d.puremagic.com/issues/show_bug.cgi?id=8408


yebblies <yebblies@gmail.com> changed:

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--- Comment #13 from yebblies <yebblies@gmail.com> 2013-01-17 01:14:02 EST ---
Is issue 8998 a regression caused by this patch?

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March 04, 2013
http://d.puremagic.com/issues/show_bug.cgi?id=8408



--- Comment #14 from github-bugzilla@puremagic.com 2013-03-03 16:07:38 PST ---
Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/ee06e4a38cb7e35fe046ffd4c5a938063c48dc30 Merge pull request #1519 from 9rnsr/fix_purity

Refactoring/improvement of issue 8408, and additionally fixing Issue 8998

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March 25, 2013
http://d.puremagic.com/issues/show_bug.cgi?id=8408



--- Comment #15 from github-bugzilla@puremagic.com 2013-03-24 20:57:04 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/b6a809346a43c7fbf350bd4181d350dd9b2cd4e6 Merge pull request #1110 from 9rnsr/fix8408

https://github.com/D-Programming-Language/dmd/commit/ee06e4a38cb7e35fe046ffd4c5a938063c48dc30 Merge pull request #1519 from 9rnsr/fix_purity

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