[Issue 17927] [scope] `scope inout` parameter value can be escaped via return (page 2)

https://issues.dlang.org/show_bug.cgi?id=17927 --- Comment #10 from Martin Nowak <code@dawg.eu> --- Thanks for investigating, so now it's reduced to the old problem that the scope system does not allow to define entry points. Of course in real life this is using malloc instead of GC'ed dup, but it's not possible to contain the former. --

https://issues.dlang.org/show_bug.cgi?id=17927 Atila Neves <atila.neves@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |atila.neves@gmail.com --- Comment #11 from Atila Neves <atila.neves@gmail.com> --- I don't understand how it's possible that making it `inout` is correct inference. This allows for code that looks @safe but isn't. This really shouldn't compile: @safe: const(int)* gInt; void main() { auto s = Struct(); gInt = s.ptr; // ARGH! } struct Struct { int* ints; this(int size) { import core.stdc.stdlib; ints = () @trusted { return cast(int*) malloc(size); }(); } ~this() { import core.stdc.stdlib; () @trusted { free(ints); }(); } scope inout(int)* ptr() inout { return ints; } } And yet it does. I guess I'll have to define 3 methods for mutable, const and immutable if I want to not crash. --

August 20, 2018

[Issue 17927] [scope] `scope inout` parameter value can be escaped via return

Posted by Steven Schveighoffer

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Steven Schveighoffer

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https://issues.dlang.org/show_bug.cgi?id=17927

Steven Schveighoffer <schveiguy@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
                 CC|                            |schveiguy@yahoo.com
         Resolution|FIXED                       |---

--- Comment #12 from Steven Schveighoffer <schveiguy@yahoo.com> ---
(In reply to Walter Bright from comment #4)
> It turns out that:
> 
>   struct String {
>     inout(char)* mem2() inout scope @safe { return ptr; }
>     char* ptr;
>   }
> 
> not issuing an error is actually correct, because a parameter that is `ref inout` is inferred to be `return`, and the `this` parameter for `mem2` is `ref inout`.


What? ref inout should NOT be inferred as return. inout is a pattern match on the mutability of the parameters, it does not necessarily imply that it is part of the return type.

This can be handy when trying avoid code duplication when the const/immutable is nested under several indirections (including ref).

Reopening, the original problem is not fixed. The error case added tests for compiling the functions, but doesn't test that the result of the inout function is scope (it should be).

--

https://issues.dlang.org/show_bug.cgi?id=17927 Les De Ridder <dlang@lesderid.net> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |dlang@lesderid.net --

https://issues.dlang.org/show_bug.cgi?id=17927 Mike Franklin <slavo5150@yahoo.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |slavo5150@yahoo.com --- Comment #13 from Mike Franklin <slavo5150@yahoo.com> --- Inferring `return` on `this` for anything marked with `inout` appears to be the cause of issue 20149. --

https://issues.dlang.org/show_bug.cgi?id=17927 Walter Bright <bugzilla@digitalmars.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|REOPENED |RESOLVED Resolution|--- |INVALID --- Comment #14 from Walter Bright <bugzilla@digitalmars.com> --- (In reply to Steven Schveighoffer from comment #12) > ref inout should NOT be inferred as return. inout is a pattern match > on the mutability of the parameters, it does not necessarily imply that it > is part of the return type. inout is deliberately inferred as return. It's the way the language currently works. To change it please make an enhancement request, as such should be discussed on its own merits. --

https://issues.dlang.org/show_bug.cgi?id=17927 Steven Schveighoffer <schveiguy@yahoo.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|INVALID |FIXED --- Comment #15 from Steven Schveighoffer <schveiguy@yahoo.com> --- Fixing the resolution, as the original bug was not invalid. If I have time, I'll try to remember what this was about and open another enhancement request. --

https://issues.dlang.org/show_bug.cgi?id=17927 Dennis <dkorpel@live.nl> changed: What |Removed |Added ---------------------------------------------------------------------------- See Also| |https://issues.dlang.org/sh | |ow_bug.cgi?id=22027 --

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