Set height of Toolbar half of attr/actionBarSize in xml

Is there anyway to set height of a "android.support.v7.widget.Toolbar" half of a predefined attr like "?android:attr/actionBarSize" in layout xml file? in fact I want the height of my toolbar be something like :

<android.support.v7.widget.Toolbar
    android:layout_width="match_parent"
    android:layout_height=("?android:attr/actionBarSize")/2
    >