使用訪問者檢查表示式的結構

通過覆蓋 ExpressionVisitor 的一些方法來定義新的訪問者類 :

class PrintingVisitor : ExpressionVisitor {
    protected override Expression VisitConstant(ConstantExpression node) {
        Console.WriteLine("Constant: {0}", node);
        return base.VisitConstant(node);
    }
    protected override Expression VisitParameter(ParameterExpression node) {
        Console.WriteLine("Parameter: {0}", node);
        return base.VisitParameter(node);
    }
    protected override Expression VisitBinary(BinaryExpression node) {
        Console.WriteLine("Binary with operator {0}", node.NodeType);
        return base.VisitBinary(node);
    }
}

呼叫 Visit 在現有表示式上使用此訪問者:

Expression<Func<int,bool>> isBig = a => a > 1000000;
var visitor = new PrintingVisitor();
visitor.Visit(isBig);