Created attachment 1795 [details]
source code

The Source Code:

    import std.stdio;
    import std.algorithm.searching : find;


    struct Classes
    {
        string[] _classes;
        alias _classes this;


        auto opBinary( string op: "in" )( string rhs )
        {
            return _classes.find( rhs );
        }
    }


    void main()
    {
        Classes cs;

        cs ~= "box";
    	writeln( cs._classes );

        auto res = "box" in cs._classes;
        writeln( res );
    }

The Goal:

   - Use overload operator "in"
   - Check string in string[]

Concrette:

   "box" in cs._classes;

Expected:

   Range r = "box" in cs._classes;
   assert( !r.empty );

Got:
   Compile time error:
       Error: incompatible types for ("box") in (cs._classes): string and string[] 


Full log:
    C:\src\dtest-op-in>dub run
    Performing "debug" build using C:\D\dmd2\windows\bin\dmd.exe for x86_64.
    dtest-op-in ~master: building configuration "application"...
    source\app.d(25,16): Error: incompatible types for ("box") in (cs._classes): string and string[]
    C:\D\dmd2\windows\bin\dmd.exe failed with exit code 1.