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### 3000. `monotonic_memory_resource::do_is_equal` uses `dynamic_cast` unnecessarily

Section: 20.12.6.3 [mem.res.monotonic.buffer.mem] Status: C++20 Submitter: Pablo Halpern Opened: 2017-07-14 Last modified: 2021-02-25

Priority: 0

View all other issues in [mem.res.monotonic.buffer.mem].

View all issues with C++20 status.

Discussion:

Section [mem.res.monotonic.buffer.mem], paragraph 11 says

>     bool do_is_equal(const memory_resource& other) const noexcept override;

> > Returns: `this == dynamic_cast<const monotonic_buffer_resource*>(&other)`.

The `dynamic_cast` adds nothing of value. It is an incorrect cut-and-paste from an example `do_is_equal` for a more complex resource.

[2017-07-16, Tim Song comments]

The pool resource classes appear to also have this issue.

[2017-09-18, Casey Carter expands PR to cover the pool resources.]

Previous resolution: [SUPERSEDED]

> 1. Edit 20.12.6.3 [mem.res.monotonic.buffer.mem] as indicated:

>    >     bool do_is_equal(const memory_resource& other) const noexcept override;

>    > > Returns: `this == dynamic_cast<const monotonic_buffer_resource*>(&other)`.

[ 2017-11-01 Moved to Tentatively Ready after 7 positive votes for P0 on c++std-lib. ]

[2018-3-17 Adopted in Jacksonville]

Proposed resolution:

This resolution is relative to N4687.

1. Edit 20.12.5.4 [mem.res.pool.mem] as indicated:

   >     bool synchronized_pool_resource::do_is_equal(const memory_resource& other) const noexcept override;
   >         const memory_resource& other) const noexcept override;

   > > Returns: `this == dynamic_cast<const synchronized_pool_resource*>(&other)`.

2. Strike 20.12.5.4 [mem.res.pool.mem] paragraph 10, and the immediately preceding declaration of `unsynchronized_pool_resource::do_is_equal`.

3. Edit 20.12.6.3 [mem.res.monotonic.buffer.mem] as indicated:

   >     bool do_is_equal(const memory_resource& other) const noexcept override;

   > > Returns: `this == dynamic_cast<const monotonic_buffer_resource*>(&other)`.