TDirectory operator= is deleted

[Nerazim]

ROOT Version: 6.24.06
Platform: Linux
Compiler: gcc

Dear ROOT developers,
TDirectory’s copy assignment operator is implicitly deleted
What would be the correct form of this code:

auto cwd = gDirectory;
gDirectory = nullptr;
//do somethings here 
gDirectory = cwd;

Regards,
Nikolay

[Wile_E_Coyote]

Using “auto” (anywhere in ROOT) means that you do not actually know what you are doing and why.
Use a proper: TDirectory *cwd = gDirectory;

BTW. @Axel You’ve introduced a real incompatibility in ROOT 6.24:

root [0] gROOT // the actual current directory
(TROOT *) 0x7feb7ee770e0
root [1] gDirectory // not a TDirectory pointer any more
(ROOT::Internal::TDirectoryAtomicAdapter) @0x5619a5d99170
root [2] (TDirectory*)gDirectory // still returns the current directory
(TDirectory *) 0x7feb7ee770e0
root [3] auto cwd = (TDirectory*)gDirectory // what is this then?
(TDirectory *) @0x7ffdaf6bdee8
root [4] TDirectory *&cwd = gDirectory // this dies
ROOT_prompt_4:1:14: error: non-const lvalue reference to type 'TDirectory *' cannot bind to a temporary of type 'ROOT::Internal::TDirectoryAtomicAdapter'
TDirectory *&cwd = gDirectory // this dies
             ^     ~~~~~~~~~~
root [5] TDirectory *&cwd = (TDirectory*)gDirectory // this dies, too
ROOT_prompt_5:1:14: error: non-const lvalue reference to type 'TDirectory *' cannot bind to a temporary of type 'TDirectory *'
TDirectory *&cwd = (TDirectory*)gDirectory // this dies, too
             ^     ~~~~~~~~~~~~~~~~~~~~~~~

[Nerazim]

Thank you @Wile_E_Coyote !

[Axel]

Hi @Wile_E_Coyote could you cross-check with printf? There’s an open bug in cling where the value printer fails with variables of point type…

[pcanal]

@Wile_E_Coyote

root [1] gDirectory // not a TDirectory pointer any more
(ROOT::Internal::TDirectoryAtomicAdapter) @0x5619a5d99170

This is not really new (end of 2020, see 085e9c182b9f639d5921c75de284ae7f20168b6e and was necessary to fix ’ #6939 gDirectory in one thread pointed to TFile deleted in another thread.')

root [3] auto cwd = (TDirectory*)gDirectory // what is this then?

The adapter has an operator TDirectory*

root [4] TDirectory *&cwd = gDirectory // this dies

Indeed this can no longer be supported (but hopefully is not actually used … ).

[pcanal]

Instead of :

@Nerazim

auto cwd = gDirectory;
gDirectory = nullptr;
//do somethings here 
gDirectory = cwd;

Use:

{
    TDirectory::TContext ctxt;  // Default to swiching the gDirectory to nullptr.
    // do somethings here 
}