@Override
    public final boolean equals(Object obj) {
        if (!super.equals(obj)) {
            return false;
        }
        if (!equalsExpression((ExpressionNode)obj)) {
            return false;
        }
        return true;
    }
Give an argument to this expression and store the result.

@param arg    Argument to use for expression.
@param result Node to contain the result.
searchlib/src/main/java/com/yahoo/searchlib/expression/ExpressionNode.java