function setVec (vec, x, y, z, w) {
    var propagate = false;

    propagate = _vecOptionalSet(vec, 0, x) || propagate;
    propagate = _vecOptionalSet(vec, 1, y) || propagate;
    propagate = _vecOptionalSet(vec, 2, z) || propagate;
    if (w != null)
        propagate = _vecOptionalSet(vec, 3, w) || propagate;

    return propagate;
}
private method to set values within an array.
Returns whether or not the array has been changed.

@method

@param {Array} vec The vector to be operated upon
@param {Number | null | undefined} x The x value of the vector
@param {Number | null | undefined} y The y value of the vector
@param {Number | null | undefined} z The z value of the vector
@param {Number | null | undefined} w the w value of the vector

@return {Boolean} whether or not the array was changed