Sorry, I think I misunderstood your problem in my last email. It is not really about friends (though it can cause troubles), but the instantiation moment. David pinned it: the function would be available as long as you instantiate S::X<256>.

 

On Thu, 5 May 2022 at 17:28, Vladimir Grigoriev via Std-Discussion <std-discussion@lists.isocpp.org> wrote:

Try this code

 

https://gcc.godbolt.org/z/Mrb3WzMv7

 

If to write

 

inline X<256> operator+(const X<256>&, const X<256>&) noexcept;

 

then the error message is

 

<source>:24: undefined reference to `S::operator+(S::X<256u> const&, S::X<256u> const&)'

 

 

 

 

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