Add const qualifier to proxy::invoke() #28
Conversation
| @@ -477,10 +478,10 @@ class sbo_ptr { | |||
| sbo_ptr(sbo_ptr&&) noexcept(std::is_nothrow_move_constructible_v<T>) | |||
| = default; | |||
|
|
|||
| T& operator*() { return value_; } | |||
| T& operator*() const { return value_; } | |||
There was a problem hiding this comment.
question: The one potential downside I see to this is here we have 'physical' const but not 'logical' const as we're returning a non-const reference by calling a const function (meaning you can then mutate the internals of the returned object after calling a const function). I've seen this referred to in the past as 'const broken' (see https://chromium.googlesource.com/chromium/src/+/HEAD/styleguide/c++/const.md#classes-of-const-in_correctness for more details). Might it be possible to provide overloads for both const and non-const versions like so...
const T& operator*() const { return value_; }
T& operator*() { return value_; }
If this is purely an implementation detail it might be fine but I just wanted to mention it incase.
There was a problem hiding this comment.
The one potential downside I see to this is here we have 'physical'
constbut not 'logical'constas we're returning a non-const reference by calling aconstfunction (meaning you can then mutate the internals of the returned object after calling aconstfunction).
In this case, value_ is considered as an internal storage of the pointee (as sbo_ptr implies "small buffer optimization"). There are many similar practices in various implementations of STL. For example, in MSVC implementation of std::function, getting the underlying object is always const, regardless of whether it points to an internal storage. The reason MSVC implementation of std::function does not use mutable is that it stores an addition pointer inside the object, which is not an optimal memory layout and makes it bigger than proxy when the buffer size for SBO is the same.
Might it be possible to provide overloads for both const and non-const versions like so...
const T& operator*() const { return value_; } T& operator*() { return value_; } >> ```
No. Doing this will let proxy choose the first overload. Users will not be able to mutate the pointee created from make_proxy when SBO is enabled.
If this is purely an implementation detail it might be fine but I just wanted to mention it incase.
Well noted! Thank you for the comments! Although it is an implementation detail, we still want to keep it as neat as we could😀. Please let us know if there is any further consideration!
No description provided.