can't link a code, is it a bug or my fault?

[Iliya]

Hello.

I am using dmd 2.094.1 on linux for compiling a piece code I 
found on the github. Unfortunately linker can't link it as it 
can't find opCall symbol instantiation demangled as:

pure nothrow @nogc @safe bool 
app.IsEqual!(char).IsEqual.opCall(in char, in char)

Do you have any ideas on:

1. Why compiler searches for such function attributes - pure 
nothrow @nogc @safe, as I don't specify them. Is this a bug or 
feature?)

2. What changes are needed to compile this rather simple example.


Please, help me!


Reference to my piece of code in app.d:

struct IsEqual(T)
{
     static bool opCall( in T p1, in T p2 )
     {
         return p1 == p2;
     }
}


size_t find(T, Pred = IsEqual!(T))
     (in T[] haystack, in T needle, Pred pred = Pred.init)
{
     foreach ( pos, cur; haystack )
     {
         if( pred( cur, needle ) )
             return pos;
     }
     return haystack.length;
}


int main(string[] args)
{
     auto pos = find("abc" , 'b');
     assert(pos == 1);

     return 0;
}


Linker error message:

Linking...
/usr/bin/ld: 
.dub/build/application-debug-linux.posix-x86_64-dmd_2094-BD99179F1B52B13DDA1C2B0172F5081E/app.bin.o: in function `_D3app__T4findTaTSQq__T7IsEqualTaZQlZQBcFNaNbNiNfIAaIaQBlZm':
source/app.d:15: undefined reference to 
`_D3app__T7IsEqualTaZQl6opCallFNaNbNiNfIaIaZb'
collect2: error: ld returned 1 exit status


ddemangle output on these symbols:

_D3app__T7IsEqualTaZQl6opCallFNaNbNiNfIaIaZb
pure nothrow @nogc @safe bool 
app.IsEqual!(char).IsEqual.opCall(in char, in char)

_D3app__T4findTaTSQq__T7IsEqualTaZQlZQBcFNaNbNiNfIAaIaQBlZm
pure nothrow @nogc @safe ulong app.find!(char, 
app.IsEqual!(char).IsEqual).find(in char[], in char, 
app.IsEqual!(char).IsEqual)


Thanks you!