Add declarations of explicit specializations and instantiations. #430
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Currently, code that uses the specializations in question will accidentally and erroneously specialize the primary template. The reason this appears to "work" is a pure accident due to the way the linker currently works. The code violates the one-definition-rule, and all programs depending on it are ill-formed, no diagnostic required (i.e. running all such programs has undefined behaviour). Additionally, declaring explicit instantiations is also good practice, since it declares intent and prevents accidental later explicit specializations (it would be an error to declare those after the extern declaration of the explicit instantiation had been seen). Explicit specializations and instantiations are declared in .hpp files near the respective template. (Found by @tkoeppe by compiling with clang -Wundefined-func-template.)
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(This is #428, but ported to v0.17.) |
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Currently, code that uses the specializations in question will
accidentally and erroneously specialize the primary template. The
reason this appears to "work" is a pure accident due to the way the
linker currently works. The code violates the one-definition-rule,
and all programs depending on it are ill-formed, no diagnostic
required (i.e. running all such programs has undefined behaviour).
Additionally, declaring explicit instantiations is also good
practice, since it declares intent and prevents accidental later
explicit specializations (it would be an error to declare those
after the extern declaration of the explicit instantiation had been
seen).
Explicit specializations and instantiations are declared in .hpp
files near the respective template.
(Found by @tkoeppe by compiling with clang -Wundefined-func-template.)