https://issues.dlang.org/show_bug.cgi?id=20968

--- Comment #1 from Per Nordlöw <per.nordlow@gmail.com> ---
Same linker error is triggered when replacing `opEquals` with `opCmp` as with


Rational!(I1) rational(I1, I2)(I1 , I2)
{
    return typeof(return)();
}

struct Rational(Int)
{
    bool opCmp(Rhs)(Rhs _) {}
}

@nogc unittest
{
    auto _ = rational(1, 2);
}


instead fails to link as

rational.o:__main.d:_D36TypeInfo_S8rational__T8RationalTiZQm6__initZ: error: undefined reference to '_D6object7_xopCmpFMxPvMxQeZb'

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https://issues.dlang.org/show_bug.cgi?id=20968

Boris Carvajal <boris2.9@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |boris2.9@gmail.com

--- Comment #2 from Boris Carvajal <boris2.9@gmail.com> ---
Just quoting forum's reply https://forum.dlang.org/thread/mftygusieubpaoobyogx@forum.dlang.org

You can get more info compiling with "-verrors=spec"

"(spec:1) Error: template rational.Rational!int.Rational.opEquals cannot deduce
function from argument types !()(const(Rational!int)) const, candidates are:"

>From reading the docs for function opEquals
(https://dlang.org/spec/operatoroverloading.html#equals).
It shows a templated version with a const modifier.
If you change the function signature to:

bool opEquals(Rhs)(Rhs _) const {return true;} // Note the 'const', and putting
some return back because dustmite removed it

The program links fine.

So it seems a compiler error is gagged that should be exposed and also could be improved.

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https://issues.dlang.org/show_bug.cgi?id=20968

FeepingCreature <default_357-line@yahoo.de> changed:

           What    |Removed                     |Added
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                 CC|                            |default_357-line@yahoo.de

--- Comment #3 from FeepingCreature <default_357-line@yahoo.de> ---
May relate to https://issues.dlang.org/show_bug.cgi?id=19091 - sometimes the compiler doesn't notice misinstantiation of structs. Then the failed struct is cached for the template parameter and treated as successful.

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https://issues.dlang.org/show_bug.cgi?id=20968

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P1                          |P3

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