[llvm] r185851 - [ADT/NullablePtr] Allow implicit conversion of NullablePtr<OtherT> -> NullablePtr<T> if OtherT is derived from T.

[David Blaikie]

On Mon, Jul 8, 2013 at 7:31 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com> wrote:
> On Jul 8, 2013, at 5:31 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>> On Mon, Jul 8, 2013 at 5:08 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com> wrote:
>>> On Jul 8, 2013, at 4:05 PM, David Blaikie <dblaikie at gmail.com> wrote:
>>>
>>> On Mon, Jul 8, 2013 at 2:51 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com>
>>> wrote:
>>>
>>> On Jul 8, 2013, at 12:47 PM, David Blaikie <dblaikie at gmail.com> wrote:
>>>
>>> On Mon, Jul 8, 2013 at 12:12 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com>
>>> wrote:
>>>
>>> Author: akirtzidis
>>> Date: Mon Jul  8 14:12:01 2013
>>> New Revision: 185851
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=185851&view=rev
>>> Log:
>>> [ADT/NullablePtr] Allow implicit conversion of NullablePtr<OtherT> ->
>>> NullablePtr<T> if OtherT is derived from T.
>>>
>>>
>>> Might be nicer to do this for any case where SrcT* is implicitly
>>> convertible DestT* (such as adding cv qualifiers or converting to
>>> void*).
>>>
>>>
>>> cv qualifiers look like are working, void* is not.
>>> In general, we need to add the equivalent of C++11's is_convertible to
>>> "llvm/Support/type_traits.h" and use it here.
>>>
>>>
>>> Shall we do that then?
>>>
>>> (your current implementation also disables this ctor for NullablePtr's
>>> of non-class type (NullablePtr<int> for example), I think... that
>>> seems unreasonable)
>>>
>>>
>>> Feel free to enhance it :-)
>>
>> Alternatively, this code doesn't seem to have any uses inside the llvm
>> codebase (at least not clang, llvm, compiler-rt, libcxx - maybe in
>> lldb?) nor any tests. Should we just remove it instead? (I assume you
>> have a use-case, or you wouldn't've been motivated to update it - is
>> that use case somewhere in the llvm project (broadly, across all
>> subprojects) or out of tree?)
>
> It is used out of tree.

It might be more suitable for it to live along with the code that's
consuming it, I'd imagine. (that'd be my preference, at least - though
if it's really necessary for it to be here, it should probably at
least have unit tests)

- David

>
>>
>> - David
>>
>>>
>>> -Argyrios
>>>
>>>
>>>
>>>
>>>
>>> Modified:
>>>  llvm/trunk/include/llvm/ADT/NullablePtr.h
>>>
>>> Modified: llvm/trunk/include/llvm/ADT/NullablePtr.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/NullablePtr.h?rev=185851&r1=185850&r2=185851&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/ADT/NullablePtr.h (original)
>>> +++ llvm/trunk/include/llvm/ADT/NullablePtr.h Mon Jul  8 14:12:01 2013
>>> @@ -14,6 +14,7 @@
>>> #ifndef LLVM_ADT_NULLABLEPTR_H
>>> #define LLVM_ADT_NULLABLEPTR_H
>>>
>>> +#include "llvm/Support/type_traits.h"
>>> #include <cassert>
>>> #include <cstddef>
>>>
>>> @@ -25,8 +26,17 @@ namespace llvm {
>>> template<class T>
>>> class NullablePtr {
>>> T *Ptr;
>>> +  struct PlaceHolder {};
>>> +
>>> public:
>>> NullablePtr(T *P = 0) : Ptr(P) {}
>>> +
>>> +  template<typename OtherT>
>>> +  NullablePtr(NullablePtr<OtherT> Other,
>>> +              typename enable_if<
>>> +                is_base_of<T, OtherT>,
>>> +                PlaceHolder
>>> +              >::type = PlaceHolder()) : Ptr(Other.getPtrOrNull()) {}
>>>
>>> bool isNull() const { return Ptr == 0; }
>>> bool isNonNull() const { return Ptr != 0; }
>>>
>>>
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>>>
>>>
>