MemberExpression.ToString() - 替换参数

Question

鉴于此方法：

public static string GetMemberIdentifier<TProp>(Expression<Func<Team, TProp>> expression)
{
    return expression.Body.ToString();
}

lambda 表达式可以转换为字符串表示形式：

var nameIdentifier1 = GetMemberIdentifier(t => t.Members[1].Name);

给出 (a):

t.Members.get_Item(1).Name

然而调用它：

var i = 0;
var nameIdentifier2 = GetMemberIdentifier(t => t.Members[i].Name);

(b) 中的结果：

t.Members.get_Item(value(Program+<>c__DisplayClass2).i).Name

是否可以使 b) 中的输出与 a) 中的输出相同？

.NET Fiddle: https://dotnetfiddle.net/cHG7H3

所需用法（简体）：

for(int i = 0; i < team.Members.Count; i++)
{
    Console.WriteLine(GetMemberIdentifier(t => t.Members[i].Name));
}

输出：

t.Members.get_Item(0).Name
t.Members.get_Item(1).Name
t.Members.get_Item(2).Name

Answer 1

如果你的 lambda 表达式要这么简单，那么你可以这样做：

public class ArgumentsTransformToConstantVisitor : ExpressionVisitor
{
    private readonly Dictionary<string, Func<object>> args;

    public ArgumentsTransformToConstantVisitor(params (string varname, Func<object> resolver)[] args)
    {
        this.args = args.ToDictionary(i => i.varname, i => i.resolver);
    }
    
    protected override Expression VisitMember(MemberExpression node)
    {
        if (node.Expression is ConstantExpression && this.args.TryGetValue(node.Member.Name, out Func<object> resolver))
            return Expression.Constant(resolver());
        
        return base.VisitMember(node);
    }

    public string GetMemberIdentifier<TProp>(Expression<Func<Team, TProp>> expression)
    {
        return ((LambdaExpression)this.Visit(expression)).ToString();
    }
}

int i = 0;

var visitor = new ArgumentsTransformToConstantVisitor(("i", () => i));

for (i = 0; i < 5; i++)
{
    Console.WriteLine(visitor.GetMemberIdentifier(t => t.Members[i].Name));
}

MemberExpression.ToString() - 替换参数

MemberExpression.ToString() - substituting parameters

c#

lambda

expression-trees