refactor: return std::nullopt instead of {} #21498

1. 
   fanquake commented at 3:28 am on March 22, 2021: member

   In #21415 we decided to return std::optional rather than {} for uninitialized values. This PR replaces the two remaining usages of {} with std::nullopt.

   As a side-effect, this also quells the spurious GCC 10.2.x warning that we’ve had reported quite a few times. i.e #21318, #21248, #20797.

   0txmempool.cpp: In member function ‘CTxMemPool::setEntries CTxMemPool::GetIterSet(const std::set<uint256>&) const’:
   1txmempool.cpp:898:13: warning: ‘<anonymous>’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   2  898 |     return {};
   3      |             ^
   

2. refactor: return std::nullopt instead of {}

   In #21415 we decided to return `std::optional` rather than `{}` for
   uninitialized values. This PR repalces the two remaining usages of `{}`
   with `std::nullopt`.
   
   As a side-effect, this also quells the spurious GCC 10.2.x warning that
   we've had reported quite a few times. i.e #21318, #21248, #20797.
   
   ```bash
   txmempool.cpp: In member function ‘CTxMemPool::setEntries CTxMemPool::GetIterSet(const std::set<uint256>&) const’:
   txmempool.cpp:898:13: warning: ‘<anonymous>’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     898 |     return {};
         |             ^
   ```

   5294f0d5a9
3. fanquake added the label Refactoring on Mar 22, 2021
4. hebasto approved
5. 
   hebasto commented at 3:53 am on March 22, 2021: member

   ACK 5294f0d5a94cc7beaf692131fba0cad8beec9f13, I have reviewed the code and it looks OK, I agree it can be merged.
6. MarcoFalke merged this on Mar 22, 2021
7. MarcoFalke closed this on Mar 22, 2021

   ---

8. fanquake deleted the branch on Mar 22, 2021
9. 
   jonatack commented at 7:05 am on March 22, 2021: member

   Posthumous ACK
10. 
    MarcoFalke commented at 7:11 am on March 22, 2021: member

    Looks like gcc-11 fixed the bug. I couldn’t reproduce the warning before and after this patch.
11. 
    jnewbery commented at 9:07 am on March 22, 2021: member

    This seems completely pointless unless you’re going to update the style guide to say that we shouldn’t use return {} to return a default-initialized object (which I don’t think we should do - there’s absolutely nothing wrong with that style and it’s used in many places in the code).
12. 
    fanquake commented at 9:09 am on March 22, 2021: member

    This seems completely pointless unless

    This was worthwhile just to stop the flow of GCC false positive reports. GCC 10.2 wont be going anywhere for a long time.

13. 
    jnewbery commented at 9:33 am on March 22, 2021: member

    This was worthwhile just to stop the flow of GCC false positive reports.

    I think that’s a slightly better motivation than “we decided to return std::optional rather than {}”

14. sidhujag referenced this in commit 9f12fb3d2e on Mar 22, 2021
15. deadalnix referenced this in commit 078ea74aa1 on Apr 6, 2022
16. DrahtBot locked this on Aug 16, 2022

Contributors
fanquake hebasto jonatack MarcoFalke jnewbery

Labels
Refactoring