Method delUse

chapter24/src/main/java/com/seaofnodes/simple/node/Node.java:237–240

( Node use )

    public boolean isDead() { return isUnused() && nIns()==0 && _type==null; }

    // Shortcuts to stop DCE mid-parse
    // Add bogus null use to keep node alive
    @SuppressWarnings("unchecked")
    public <N extends Node> N keep() { addUse(null); return (N)this; }
    // Remove bogus null.
    @SuppressWarnings("unchecked")
    public <N extends Node> N unkeep() { delUse(null); return (N)this; }