如何为unchecked-statement创建表达式树语句

Question

在我的表达式树(使用Expression类创建)中,我需要将我的代码包装在一个未经检查的块中(http://msdn.microsoft.com/en-us/library/a569z7k8.aspx)但是如何？这种Expression类型没什么有趣的.

Answer 1

该Expression类型具有每个运算符的单独版本,用于已检查和未检查的操作.要将checked表达式体内的任何操作更改为unchecked操作,您不能将整个事物包装在unchecked表达式中.您需要遍历整个表达式树,查找已检查操作的所有用法,并将这些操作替换为未经检查的版本.

public static Expression MakeUnchecked(this Expression expression)
{
    return new UncheckedExpressionVisitor().Visit(expression);
}

public class UncheckedExpressionVisitor : ExpressionVisitor
{
    protected override Expression VisitBinary(BinaryExpression node)
    {
        switch (node.NodeType)
        {
            case ExpressionType.AddAssignChecked:
                return base.Visit(Expression.AddAssign(node.Left, node.Right));
            case ExpressionType.AddChecked:
                return base.Visit(Expression.Add(node.Left, node.Right));
            case ExpressionType.MultiplyAssignChecked:
                return base.Visit(Expression.MultiplyAssign(node.Left, node.Right));
            case ExpressionType.MultiplyChecked:
                return base.Visit(Expression.Multiply(node.Left, node.Right));
            case ExpressionType.SubtractAssignChecked:
                return base.Visit(Expression.SubtractAssign(node.Left, node.Right));
            case ExpressionType.SubtractChecked:
                return base.Visit(Expression.Subtract(node.Left, node.Right));
            default:
                return base.VisitBinary(node);
        }
    }

    protected override Expression VisitUnary(UnaryExpression node)
    {
        switch (node.NodeType)
        {
            case ExpressionType.ConvertChecked:
                return base.Visit(Expression.Convert(node.Operand, node.Type));
            case ExpressionType.NegateChecked:
                return base.Visit(Expression.Negate(node.Operand, node.Method));
            default:
                return base.VisitUnary(node);
        }
    }
}