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Niels Lohmann
2edeefaa43
The bounded-descent copy added by #5389 built the elements of a deep copy (nested past the 128-level bound) by default-constructing them and then having copy_metadata() assign their base class afterwards. That assignment is only instantiated for values nested past the bound, but being called from copy_structured() at all meant it was compiled for every copy, so a CustomBaseClass that is copy-constructible but not move-assignable (for example one with a const data member) no longer let its basic_json be copy-constructed, at any depth. copy_array_level() and copy_object_level() now build each element with a private-tag-selected constructor that copy-constructs the base class (and, under JSON_DIAGNOSTIC_POSITIONS, copies the positions) directly, the same way the copy constructor already builds elements within the 128-level bound. Copying a basic_json is therefore back to requiring only a copy-constructible base class, as documented and as it was before #5389; copy assignment is unchanged and still requires an assignable one. Fixes #5674. Signed-off-by: Niels Lohmann <mail@nlohmann.me>