[Issue 14781] impure delegate to pure function context should be able to modify context

Jul 07, 2015

Kenji Hara

Jul 08, 2015

Jul 08, 2015

Jul 08, 2015

Jul 08, 2015

Jul 08, 2015

https://issues.dlang.org/show_bug.cgi?id=14781 Kenji Hara <k.hara.pg@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |pull --- Comment #2 from Kenji Hara <k.hara.pg@gmail.com> --- https://github.com/D-Programming-Language/dmd/pull/4808 --

https://issues.dlang.org/show_bug.cgi?id=14781 Denis Shelomovskij <verylonglogin.reg@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |verylonglogin.reg@gmail.com --- Comment #3 from Denis Shelomovskij <verylonglogin.reg@gmail.com> --- (In reply to Steven Schveighoffer from comment #0) > In a followup to issue 9148, which made this illegal: > > int impureFuncCall() { static int g; return g; } > auto foo(out int delegate() pure pureDg) pure { > int x; > auto bar()() { > impureFuncCall(); > x = 1; // Error: impure function 'bar' cannot access variable > 'x' > // declared in enclosing pure function 'foo' > } > > pureDg = &(bar!()); > > int dg() pure { return x;} > return &dg; > } > > > This should be allowed. > ... Do you mean this code should compile? If so, either pure function `bar` can call an impure function or impure delegate is implicitly convertible to a pure one. If you are opening an issue with an enhancement please provide a clear and concise testcase. Thanks. --

https://issues.dlang.org/show_bug.cgi?id=14781 --- Comment #4 from Steven Schveighoffer <schveiguy@yahoo.com> --- (In reply to Denis Shelomovskij from comment #3) > Do you mean this code should compile? Yes. > If so, either pure function `bar` can > call an impure function or impure delegate is implicitly convertible to a > pure one. No, but I made an error in the example from what I meant. should be: auto foo(out int delegate() impureDg) pure { ... impureDg = &(bar!()); > If you are opening an issue with an enhancement please provide a clear and concise testcase. Thanks. It's hard to make a test case that "should compile" without making an error with no compiler to help you :D Really, the issue is that bar doesn't compile, not that the impure delegate can't be assigned. --

https://issues.dlang.org/show_bug.cgi?id=14781 --- Comment #5 from Denis Shelomovskij <verylonglogin.reg@gmail.com> --- (In reply to Steven Schveighoffer from comment #4) > (In reply to Denis Shelomovskij from comment #3) > > > Do you mean this code should compile? > > Yes. > > > If so, either pure function `bar` can > > call an impure function or impure delegate is implicitly convertible to a > > pure one. > > No, but I made an error in the example from what I meant. > > should be: > > auto foo(out int delegate() impureDg) pure { > > ... > > impureDg = &(bar!()); > > > If you are opening an issue with an enhancement please provide a clear and concise testcase. Thanks. > > It's hard to make a test case that "should compile" without making an error with no compiler to help you :D > > Really, the issue is that bar doesn't compile, not that the impure delegate can't be assigned. Then this function isn't strongly pure anymore: --- T f() pure; --- if `T` is `int delegate()`. Is everybody OK with this? --

July 08, 2015

[Issue 14781] impure delegate to pure function context should be able to modify context

Posted by ag0aep6g@gmail.com

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ag0aep6g@gmail.com

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https://issues.dlang.org/show_bug.cgi?id=14781

ag0aep6g@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ag0aep6g@gmail.com

--- Comment #6 from ag0aep6g@gmail.com ---
(In reply to Denis Shelomovskij from comment #5)
> Then this function isn't strongly pure anymore:
> ---
> T f() pure;
> ---
> if `T` is `int delegate()`.
> 
> Is everybody OK with this?

I think that's already not strongly pure. `int delegate()` has a mutable indirection in the context pointer. So a function that returns such a delegate can't be strongly pure.

See http://klickverbot.at/blog/2012/05/purity-in-d/#indirections_in_the_return_type

An example with the delegate type:
----
struct S
{
    int x = 1;
    int method() {return x++;}
}

int delegate() f() pure
{
    return &(new S).method;
}

void main()
{
   auto dg1 = f();
   version(all) auto dg2 = f();
   else auto dg2 = dg1; /* This would be equivalent to the above if f were
strongly pure. */

   import std.stdio;
   writeln(dg1()); /* "1" */
   writeln(dg1()); /* "2" */
   writeln(dg2()); /* "1" or "3", depending on the version above */
}
----

--

https://issues.dlang.org/show_bug.cgi?id=14781 Kenji Hara <k.hara.pg@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |rejects-valid Summary|impure delegate to pure |[REG2.067] impure delegate |function context should be |to pure function context |able to modify context |should be able to modify | |context Severity|enhancement |regression --- Comment #7 from Kenji Hara <k.hara.pg@gmail.com> --- I change the importance to regression, because the introduced behavior since 2.067 rejects valid code. --

https://issues.dlang.org/show_bug.cgi?id=14781 --- Comment #9 from github-bugzilla@puremagic.com --- Commits pushed to stable at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/922d79a43ff60ed324e32e2f4be1430de209746f fix Issue 14781 - impure delegate to pure function context should be able to modify context https://github.com/D-Programming-Language/dmd/commit/b30556bf2ce1b4e49fdba51ea759725c2fc6e48f Merge pull request #4970 from 9rnsr/fix14781 [REG2.067/2.068] Issue 14781 & 14962 - fix problematic purity inference introduced in #3626 --

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