获取将变量传递给参数的原始名称



要清楚,这是不是这个问题的重复。显然,我可以使用nameof操作员获取变量或参数的名称;我知道。但是,有没有办法获得传递给方法的变量的 ointer 名称?目前,我必须这样做:

static void Foo(string someVariable, string variableName)
{
    if (!FulfilsCondition(someVariable))
        Console.WriteLine($"{variableName} is bad!");
    // More code
}

我这样称呼:

string bar = string.Empty;
Foo(bar, nameof(bar));    // Or...
//Foo(bar, "bar");

,但我正在寻找一种避免反复提供变量名称的方法,而是使用类似的方法:

Foo(bar);

在这种情况下, Foo是:

static void Foo(string someVariable)
{
    string variableName = GetOriginalVariableName(someVariable);
    //  Is this possible? ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ 
    if (!FulfilsCondition(someVariable))
        Console.WriteLine($"{variableName} is bad!");
    // More code
}

是否可以在.net中可以实现?


更新:

我没有想到传递给Foo的可能性可能是一种表达方式,而不是其他人在评论中建议的变量。现在考虑一下,似乎不可能实现我无法(某种程度上)保证会有变量的东西吗?听起来像是远射,TBH,但也许那里有一个解决方案。

更新#2:

人们问我实际上要实现的目标。好吧,这与上面的第一个方法非常相似,但是如果要帮助的话,这是我正在使用的实际方法:

static bool ExceedsLimit(string s, int maxLength, string variableName,
                         out string errorMessage)
{
    if (s.Length > maxLength)
    {
        errorMessage = $"'{variableName}' must be {maxLength} characters at most.";
        return true;
    }
    errorMessage = null;
    return false;
}

,我在这样的东西中使用它:

static bool TestMethod(out bool failReason)
{
    if (ExceedsLimit(obj.Prop1, 100, nameof(obj.Prop1), out failReason)) return false;
    if (ExceedsLimit(obj.Prop2, 50, nameof(obj.Prop2), out failReason)) return false;
    if (ExceedsLimit(obj.Prop3, 80, nameof(obj.Prop3), out failReason)) return false;
    // ...
}

,但我正在寻找一种避免反复提供变量名称的方法。

您要寻找的工作要比传递param名称慢得多。

,但可以解决方法。我为您的问题疯狂,发现了一些东西。它有限制。例如仅处理本地变量。(但可以扩展以解决其他情况)。它需要PDB文件和ILDASM工具。(这似乎是获得IL的最简单方法,但也许可以通过框架功能获得)。而且非常慢。但有效)只需调用paramnamehelper.getoriginalvariablename(字符串paramname)。

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Reflection;
namespace TestParamHelper
{
    class Program
    {
        static void Main(string[] args)
        {
            new CallingClass().CallTargetMethod();
        }
    }
    public class CallingClass
    {
        public void CallTargetMethod()
        {
            var s = "str";
            var i = 5;
            new TargetClass().TargetMethod(s, i);
        }
    }
    public class TargetClass
    {
        public void TargetMethod(string strArg, int intArg)
        {
            var paramName = nameof(strArg);
            // HERE IT IS!!!
            var originalName = ParamNameHelper.GetOriginalVariableName(paramName);
            Console.WriteLine($"{originalName} is passed as {paramName}");
        }
    }
    public static class ParamNameHelper
    {
        public static string GetOriginalVariableName(string paramName)
        {
            var stackTrace = new StackTrace(true);
            var targetMethod = stackTrace.GetFrame(1).GetMethod();
            var paramIndex = targetMethod.GetParameters().ToList().FindIndex(p => p.Name.Equals(paramName));
            var callingMethod = stackTrace.GetFrame(2).GetMethod();
            var il = callingMethod.GetMethodBodyIL();
            var localIndex = il
                .TakeWhile(s => !s.Contains($"{targetMethod.DeclaringType.FullName}::{targetMethod.Name}"))
                .Reverse()
                .TakeWhile(s => s.Contains("ldloc"))
                .Reverse()
                .ElementAt(paramIndex)
                .Split('.')
                .Last();
            return il
                .SkipWhile(s => !s.Contains("locals init"))
                .TakeWhile(s => s.Contains(",") || s.Contains(")"))
                .First(s => s.Contains($"[{localIndex}]"))
                .Replace(")", "")
                .Replace(",", "")
                .Split(' ')
                .Last();
        }
    }
    internal static class MethodBaseExtensions
    {
        // improve providing location, may be via config
        private static readonly string ildasmLocation = Path.GetFullPath(@"C:Program Files (x86)Microsoft SDKsWindowsv10.0AbinNETFX 4.7.2 Toolsildasm.exe");
        internal static IEnumerable<string> GetMethodBodyIL(this MethodBase method)
        {
            var assemblyLocation = method.DeclaringType.Assembly.Location;
            var ilLocation = $"{assemblyLocation}.il";
            Process.Start(new ProcessStartInfo(ildasmLocation, $"{assemblyLocation} /output:{ilLocation}") { UseShellExecute = false })
                .WaitForExit();
            var il = File.ReadAllLines(ilLocation)
                .SkipWhile(s => !s.Contains(method.Name))
                .Skip(2)
                .TakeWhile(s => !s.Contains($"end of method {method.DeclaringType.Name}::{method.Name}"));
            File.Delete(ilLocation);
            return il;
        }
    }
}

输出:S通过Strarg

传递

否,这是不可能的,因为一种方法无法知道其参数的名称在哪里。AKA Foo无法知道它是被称为Foo(bar)还是Foo(baz)。您所做的就是使用CallerMemberName获取所调用方法的名称。例如:

static void Foo(string someVariable, [CallerMemberName] string methodName = "")
{
    if (!FulfilsCondition(someVariable))
        Console.WriteLine($"{methodName} passed a bad paramter!");
    // More code
}
static void BadMethod()
{
    string wrong = "";
    Foo(wrong);
}

将打印:

BadMethod passed a bad paramter!

您可以将Mono.Cecil用于此目的。您还需要MonoCecilReader和此答案中的其他类型和.pdb文件才能获取本地变量的名称。

ammend MethodDefinitionExtensions
public static Instruction GetInstruction(this MethodDefinition method, int offset) =>
    method
    .Body
    .Instructions
    .SingleOrDefault(i => i.Offset == offset);

创建ResolvedArgument类:

public class ResolvedArgument
{
    public string Argument { get; }
    public string Parameter { get; }
    public ResolvedArgument(string argument, string parameter) =>
        (Argument, Parameter) = (argument, parameter);
    public override string ToString() =>
        $"'{Argument}' passed for '{Parameter}'";
}

然后用方法创建静态类VariableHelper

public static ResolvedArgument ResolveArgument(object parameter)
{
    var trace = new StackTrace();
    var frame = trace.GetFrame(1);
    var method = frame.GetMethod().GetMethodDefinition();
    var arg = GetParameter(frame, method);
    frame = trace.GetFrame(2);
    return GetPassedValue(frame, method, arg);
}

其中 GetParameter是:

private static ParameterDefinition GetParameter(StackFrame frame, MethodDefinition method)
{
    var instruction = method.GetInstruction(frame.GetILOffset());
    if (instruction.IsBoxing())
        instruction = instruction.Previous;
    if (!instruction.IsLoadArg())
        throw new NotSupportedException($"Attempt to handle {instruction.OpCode}");
    if (instruction.OpCode.Code == Code.Ldarg_S)
        return (ParameterDefinition)instruction.Operand;
    var index = instruction.GetArgIndex(!method.IsStatic);
    return method.Parameters[index];
}

GetPassedValue是:

private static ResolvedArgument GetPassedValue(StackFrame frame, MethodDefinition method, ParameterDefinition parameter)
{
    var info = frame.GetMethod();
    var caller = info.GetMethodDefinition();
    var instruction = caller.GetInstruction(frame.GetILOffset());
    while (instruction != null)
    {
        if (instruction.IsCall() &&
            instruction.Operand is MethodDefinition md &&
            md.FullName.Equals(method.FullName))
                break;
        instruction = instruction.Previous;
    }
    if (instruction == null)
        throw new Exception("Not supposed to get here.");
    var il = caller
        .Body
        .Instructions
        .TakeWhile(i => i.Offset != instruction.Offset)
        .Reverse()
        .Where(i => !i.IsBoxing() && (caller.IsStatic || i.OpCode.Code != Code.Ldarg_0))
        .TakeWhile(i =>i.IsLoad())
        .Reverse()
        .ToList();
    if (il.Count != method.Parameters.Count)
        throw new NotSupportedException("Possible attempt to pass an expression");
    instruction = il[parameter.Index];
    var name = "<failed to resolve>";
    if (instruction.IsLoadArg())
    {
        var index = instruction.GetArgIndex(!caller.IsStatic);
        name = caller.Parameters.Single(p => p.Index == index).Name;
    }
    if (instruction.IsLoadField())
        name = ((FieldDefinition)instruction.Operand).Name;
    if (instruction.IsLoadLoc())
    {
        var index = instruction.GetLocIndex();
        var locals = new MonoCecilReader().Read(info);
        name = locals.Single(loc => loc.Index == index).Name;
    }
    return new ResolvedArgument(name, parameter.Name);
}

Instruction的扩展方法是:

internal static class InstructionExtensions
{
    public static bool IsCall(this Instruction instruction)
    {
        var code = instruction.OpCode.Code;
        return code == Code.Call ||
               code == Code.Callvirt;
    }
    public static bool IsBoxing(this Instruction instruction) =>
        instruction.OpCode.Code == Code.Box;
    public static bool IsLoadArg(this Instruction instruction)
    {
        var code = instruction.OpCode.Code;
        return code == Code.Ldarg_0 ||
               code == Code.Ldarg_1 ||
               code == Code.Ldarg_2 ||
               code == Code.Ldarg_3 ||
               code == Code.Ldarg_S;
    }
    public static bool IsLoadLoc(this Instruction instruction)
    {
        var code = instruction.OpCode.Code;
        return code == Code.Ldloc_0 ||
               code == Code.Ldloc_1 ||
               code == Code.Ldloc_2 ||
               code == Code.Ldloc_3 ||
               code == Code.Ldloc_S;
    }
    public static bool IsLoadField(this Instruction instruction)
    {
        var code = instruction.OpCode.Code;
        return code == Code.Ldfld ||
               code == Code.Ldsfld;
    }
    public static int GetArgIndex(this Instruction instruction, bool isInstance)
    {
        if (instruction.OpCode.Code == Code.Ldarg_S)
            return ((ParameterDefinition)instruction.Operand).Index;
        var index = -1;
        var code = instruction.OpCode.Code;
        if (code == Code.Ldarg_0)
            index = 0;
        else if (code == Code.Ldarg_1)
            index = 1;
        else if (code == Code.Ldarg_2)
            index = 2;
        else if (code == Code.Ldarg_3)
            index = 3;
        if (index != -1 && isInstance)
            index--;
        return index;
    }
    public static int GetLocIndex(this Instruction instruction)
    {
        if (instruction.OpCode.Code == Code.Ldloc_S)
            return ((VariableDefinition)instruction.Operand).Index;
        var code = instruction.OpCode.Code;
        if (code == Code.Ldloc_0)
           return 0;
        if (code == Code.Ldloc_1)
            return 1;
        if (code == Code.Ldloc_2)
            return 2;
        if (code == Code.Ldloc_3)
            return 3;
        return -1;
    }
    public static bool IsLoad(this Instruction instruction) =>
        instruction.IsLoadArg() ||
        instruction.IsLoadLoc() ||
        instruction.IsLoadField();
}

用法:

class Program
{
    private static readonly Guid sFld1 = default(Guid);
    private readonly DateTime iFld1 = default(DateTime);
    private static readonly Guid sFld2 = default(Guid);
    private readonly DateTime iFld2 = default(DateTime);
    static void Main(string[] args)
    {
        new Program().Run("_1", "_2");
    }
    private void Run(string arg1, string arg2)
    {
        int loc1 = 42;
        int loc2 = 24;
        Console.WriteLine("tFirst call");
        Method(p1: loc1, p2: arg1, p3: sFld1, p4: iFld1);
        Console.WriteLine("tSecond call");
        Method(p1: loc2, p2: arg2, p3: sFld2, p4: iFld2);
    }
    private void Method(int p1, string p2, object p3, DateTime p4)
    {
        Console.WriteLine(VariableHelper.ResolveArgument(p1));
        Console.WriteLine(VariableHelper.ResolveArgument(p2));
        Console.WriteLine(VariableHelper.ResolveArgument(p3));
        Console.WriteLine(VariableHelper.ResolveArgument(p4));
    }
}

给出:

        First call
'loc1' passed for 'p1'
'arg1' passed for 'p2'
'sFld1' passed for 'p3'
'iFld1' passed for 'p4'
        Second call
'loc2' passed for 'p1'
'arg2' passed for 'p2'
'sFld2' passed for 'p3'
'iFld2' passed for 'p4'

上述解决方案主要是可能性的证明。它比简单地传递变量的名称要慢得多。

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