MSVC build errors > C2280

C2280: attempting to reference a deleted function

error C2280: 'std::unique_ptr<Widget,std::default_delete<Widget>>::unique_ptr(const std::unique_ptr<Widget,std::default_delete<Widget>> &)': attempting to reference a deleted function

The code calls a function that is deleted, most often the copy constructor or the copy assignment of a type that can only be moved.

Causes and fixes

1. A move-only object is copied. std::unique_ptr, std::thread, and std::mutex cannot be copied: pass them by reference, or transfer them with std::move.
2. A class that contains one is copied. A class with a unique_ptr member is move-only too: move it into containers (push_back(std::move(item)) or emplace_back), or define its copy yourself.
3. A lambda that owns one is stored in std::function. std::function requires a copyable callable: use std::move_only_function in C++23, or a std::shared_ptr.
4. A member makes assignment impossible. A const or reference member deletes the copy assignment: assign member by member, or store a pointer.

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Related errors: C2440. See all guides.