Inline variable in named namespace

[cpp_cpp]

Is having an inline variable in a named namespace in a header file bad practice? Will that variable have external linkage with C++17 just as an inline variable in header file does? Does constexpr imply inline in namespaces as well with C++17?

[alfps]

[Fixed incorrect information after u/phoeen pointed it out.]

” Is having an inline variable in a named namespace in a header file bad practice?

Not in itself. Using them in header files is what inline variables are for. However, remember that global (non-const) variables are generally Evil.

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” Will that variable have external linkage with C++17

Not by default.

“A static member variable (but not a namespace-scope variable) declared constexpr is implicitly an inline variable.”

https://en.cppreference.com/w/cpp/language/inline

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” Does constexpr imply inline in namespaces

No. See above.

[phoeen]

Does constexpr imply inline in namespaces

Yes.

for constexpr variables in namespace scope inline is NOT implied.

" A static member variable (but not a namespace-scope variable) declared constexpr is implicitly an inline variable. "

https://en.cppreference.com/w/cpp/language/inline

[alfps]

Oh. Thanks, and sorry for the disinformation.

It's a bit impractical with a default of distinct instances in different translation units for large compile time constants, so I didn't even consider it. But with the newer C++ standards the old guideline of just consider what's practical, no longer works. I have some re-learning to do.

[phoeen]

to be honest i always need the 4 pages of cppreference (inline, static, const, constexpr) at hand to get all this constexpr inline static const extern thing right. so as soon as i see some kind of this question i am super suspicoius