https://issues.dlang.org/show_bug.cgi?id=22110

          Issue ID: 22110
           Summary: isCallable fails for template opCall without any
                    templated argument
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: lsferreira169@gmail.com

struct Foo
{
    auto opCall()() { return 1; }
}

isCallable!Foo is reporting false and it is actually true, because Foo() is
possible.

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