Hello
I have struct in one module (vector.d)

struct vec(string S, T=double)
    if( is(T:real) && onlyASCII(S) )
{
    private T[S.length] _data;
    alias vec!(S,T) ttype;
    alias _data this;

    mixin _workaround4424;

    auto opAssign(E)( E[] b ) if( is( E : T ) )
    {
        if( b.length != S.length ) throw new Exception("bad length");
        foreach( i, ref m; _data ) m = b[i]; return this;
    }

    auto opAssign(E)( E[S.length] b ) if( is( E : T ) )
    { foreach( i, ref m; _data ) m = b[i]; return this; }

}

and I want to use this in other module

struct mPoint(string S,T=double)
{
    alias vec!(S,T) vect;
    private union
    {
        T[S.length*2] _raw;
        vect[2] _vects;
    }
    alias _raw this;

    @property vect pos(){ return _vects[0]; }
    @property void pos( vect b ){ _vects[0] = b; } //#1

    @property vect vel(){ return _vects[1]; }
    @property void vel( vect b ){ _vects[1] = b; } //#2
}

when compile I have error
#1 Error: undefined identifier '_data'
#2 Error: undefined identifier '_data'

why code in mPoint want use identifier _data?
unittests in vector.d use all of overriding operators well.

may it associate with aliasing of vec to array?
or it associate with overriding opAssign?

solved. its associated with access private for _data field.
if I use alias compiler must replace call "a" (for my type) to "a._data" if it needs...