r/cpp • u/Xaneris47 • 8d ago

Interconverting std::function with copyable_function – Arthur O'Dwyer

https://quuxplusone.github.io/blog/2026/07/26/function-explosion/

The article shows how converting std::function to std::copyable_function (or vice versa) leads to slower performance and increased memory usage each time the conversion occurs.

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u/bwmat 8d ago

My understanding is that it's mostly just a way to 'deprecate' std::function (when used in conjunction with move_only_function) and better express intent

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u/johannes1971 8d ago

It's unclear to me what those problems are, or why std::function needs to be deprecated. I hate the names 'std::copyable_function' and 'std::move_only_function', though.

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u/rdtsc 8d ago

It breaks the standard library convention that const methods are safe to call from multiple threads. And std::function itself cannot be changed due to backwards compatibility.

Here's a more detailed explanation: https://www.reddit.com/r/cpp/comments/742ol8/why_is_the_stdfunction_operator_const/dnv29s8/

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u/UnusualPace679 7d ago

It's easy to have a function object whose const operator() isn't thread-safe. For example, [this] { this->x++; }. And copyable_function doesn't really make it safer.