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…ause ref<Derived> was already implicitly convertible to ref<Base>, but the mechanism was unclear and error messages for rejected downcasts were more cryptic than necessary. This change: - Adds RefImplicitlyUpcastableTo concept to constrain the conversion operator, making the intent explicit and improving error messages - Documents .cast() and .dynamic_pointer_cast() as alternatives for explicit downcasting - Adds unit tests for covariance behavior
When ref::cast() fails, the error message was cryptic ("null pointer
cast to ref"). Now it throws a proper bad_ref_cast (a std::bad_cast
subclass) with a clear message showing the actual types involved:
ref<nix::Base> cannot be cast to ref<nix::Derived>
This also adds a demangle.hh utility.
Ericson2314
approved these changes
Feb 16, 2026
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Motivation
Wasn't sure whether implicit upcasts were supported, then found some room for improvement and clarification.
ref was already implicitly convertible to ref, but the
mechanism was unclear and error messages for rejected downcasts were
more cryptic than necessary.
When ref::cast() fails, the error message was also cryptic ("null pointer
cast to ref"). Now it throws bad_ref_cast (a std::bad_cast subclass)
with a clear message showing the actual types involved.
Context
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