c# - 如何使匿名类仅使用 std 实现接口?
问题描述
这是我试图用 C# 重写的示例 Scala 代码:
trait FuncHolder[T, TResult] {
def Value: Function1[T, TResult]
}
object FuncHolder {
def GetFunctionHolder[T, TResult](func: Function1[T, TResult]) = new FuncHolder[T, TResult] {
override def Value: Function1[T, TResult] = func
}
}
这是我开始的地方:
public abstract class FuncHolder<T, TResult>
{
public Func<T, TResult> Value { get; }
protected FuncHolder(Func<T, TResult> value)
{
Value = value;
}
}
public static class FuncHolder
{
public static FuncHolder<T, TResult> GetFuncHolder<T, TResult>(Func<T, TResult> func)
{
var ilBody = func.Method.GetMethodBody().GetILAsByteArray();
}
}
但是后来我卡住了,因为我不确定我是否可以只复制那个字节数组il.emit
并且它会起作用。所以我想也许在 2019 年有一些方法可以在没有肮脏魔法、后期锐化输出二进制文件或其他东西的情况下实现它。我正在寻找 BCL 和 Expressions/DynamicMethods 方面的纯解决方案。
最近的尝试如下:
public abstract class FuncHolder<T, TResult>
{
public abstract TResult GetResult(T value);
}
public static class FuncHolder
{
private static ModuleBuilder _builder = AssemblyBuilder
.DefineDynamicAssembly(new AssemblyName("OmsCodegen"), AssemblyBuilderAccess.Run)
.DefineDynamicModule("MainModule");
/// <summary>
/// Returns a holder that allows safely pass delegates through the network
/// </summary>
/// <param name="func">Func to hold. Note that it must be pure function, closure with external dependencies will fail</param>
public static FuncHolder<T, TResult> GetFuncHolder<T, TResult>(Func<T, TResult> func)
{
var tb = _builder.DefineType($"<{func.Method.MetadataToken}>__FuncHolder", TypeAttributes.Class | TypeAttributes.Sealed);
tb.SetParent(typeof(FuncHolder));
var baseMethod = typeof(FuncHolder<,>).GetMethod("GetResult");
Debug.Assert(baseMethod != null);
var implementation = tb.DefineMethod(baseMethod.Name, MethodAttributes.Public | MethodAttributes.Virtual);
CopyIl(implementation, func.Method);
tb.DefineMethodOverride(implementation, baseMethod);
tb.DefineDefaultConstructor(MethodAttributes.Public | MethodAttributes.SpecialName |
MethodAttributes.RTSpecialName);
return (FuncHolder<T, TResult>) Activator.CreateInstance(tb.CreateTypeInfo().AsType());
}
private static void CopyIl(MethodBuilder implementation, MethodInfo methodInfo)
{
var ilGenerator = implementation.GetILGenerator();
var methodBody = methodInfo.GetMethodBody();
var il = methodBody?.GetILAsByteArray() ?? throw new InvalidOperationException("Cannot get method body");
foreach (var local in methodBody.LocalVariables)
ilGenerator.DeclareLocal(local.LocalType);
var opCodes = GetOpCodes(il);
for (int i = 0; i < opCodes.Length; ++i)
{
if (!opCodes[i].code.HasValue)
continue;
OpCode opCode = opCodes[i].code.Value;
if (opCode.OperandType == OperandType.InlineBrTarget)
{
ilGenerator.Emit(opCode, BitConverter.ToInt32(il, i + 1));
i += 4;
continue;
}
if (opCode.OperandType == OperandType.ShortInlineBrTarget)
{
ilGenerator.Emit(opCode, il[i + 1]);
++i;
continue;
}
if (opCode.OperandType == OperandType.InlineType)
{
Type tp = methodInfo.Module.ResolveType(BitConverter.ToInt32(il, i + 1), methodInfo.DeclaringType.GetGenericArguments(), methodInfo.GetGenericArguments());
ilGenerator.Emit(opCode, tp);
i += 4;
continue;
}
if (opCode.FlowControl == FlowControl.Call)
{
MethodInfo mi = methodInfo.Module.ResolveMethod(BitConverter.ToInt32(il, i + 1)) as MethodInfo;
if (mi == methodInfo)
ilGenerator.Emit(opCode, implementation);
else
ilGenerator.Emit(opCode, mi);
i += 4;
continue;
}
ilGenerator.Emit(opCode);
}
}
static OpCodeContainer[] GetOpCodes(byte[] data)
{
List<OpCodeContainer> opCodes = new List<OpCodeContainer>();
foreach (byte opCodeByte in data)
opCodes.Add(new OpCodeContainer(opCodeByte));
return opCodes.ToArray();
}
class OpCodeContainer
{
public OpCode? code;
byte data;
public OpCodeContainer(byte opCode)
{
data = opCode;
try
{
code = (OpCode)typeof(OpCodes).GetFields().First(t => ((OpCode)(t.GetValue(null))).Value == opCode).GetValue(null);
}
catch
{
// if it throws an exception then code should remain null
}
}
}
}
由于 CLR 执行错误而失败。
解决方案
这不完全是我想要的,但这是我带来的唯一解决方案
public abstract class FuncHolder<T, TResult>
{
[JsonIgnore]
public abstract Func<T, TResult> Value { get; }
}
public static class FuncHolder
{
private static Dictionary<int, object> _metadataTokenToMethodDictionary = new Dictionary<int, object>();
private class FuncHolderImplementation<T, TResult> : FuncHolder<T, TResult>
{
public int MetadataToken { get; }
public FuncHolderImplementation(int metadataToken)
{
MetadataToken = metadataToken;
}
public override Func<T, TResult> Value => (Func<T, TResult>)_metadataTokenToMethodDictionary[MetadataToken];
}
public static FuncHolder<T, TResult> GetFuncHolder<T, TResult>(Func<T, TResult> func)
{
if (!_metadataTokenToMethodDictionary.ContainsKey(func.Method.MetadataToken))
{
_metadataTokenToMethodDictionary[func.Method.MetadataToken] = func;
}
return new FuncHolderImplementation<T, TResult>(func.Method.MetadataToken);
}
}
我没有将函数包装在类型中,而是传递了一个 metadataToken,然后我将其转换回来。
为什么需要这个可能如下所示:
var holder = FuncHolder.GetFuncHolder<string, int>(s => s.Length);
var settings = new JsonSerializerSettings {TypeNameHandling = TypeNameHandling.All};
var json = JsonConvert.SerializeObject(holder, settings);
var holder2 = JsonConvert.DeserializeObject<FuncHolder<string, int>>(json, settings);
Console.WriteLine(holder2.Value("hello"));
如您所见,这种方式函数回调可能会被序列化和反序列化。
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