https://issues.dlang.org/show_bug.cgi?id=18960

          Issue ID: 18960
           Summary: Function parameter requires name with default value
           Product: D
           Version: D2
          Hardware: x86
                OS: All
            Status: NEW
          Severity: trivial
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: alphaglosined@gmail.com

As per spec this should not be possible.

void main() {
    Foo foo = &bar;
    foo();
}

alias Foo = void function(int=6);

void bar(int v = 6) {
    import std.stdio;
    writefln("%i", v);
}

A simple error check can be added here: https://github.com/dlang/dmd/blob/master/src/dmd/parse.d#L2860

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