c# - 在常规阵列上测试 foreach 框/拆箱？

Question

我已阅读 this excellent question关于如何定期int[]在 foreach 下处理(框与否)循环。

Array确实实现了非泛型 IEnumerable所以它必须使用 object内部(而不是 int)

但它turns out那 - 在运行时它实际上被处理为 IEnumerable<T>

如何通过简单的 C# 测试/证明(没有拳击)它代码？ (而不是通过阅读 IL。)

Answer 1

我喜欢@phoog 的回答，所以只是为了好玩:)

助手类

public static class ILUtils
{
    private static Dictionary<short, OpCode> s_opcodes = new Dictionary<short, OpCode>();

    static ILUtils()
    {
        FieldInfo[] opCodeFields = typeof(OpCodes).GetFields(BindingFlags.Public | BindingFlags.Static);
        foreach (FieldInfo opCodeField in opCodeFields)
        {
            if (opCodeField.FieldType != typeof(OpCode))
                continue;

            OpCode opcode = (OpCode)opCodeField.GetValue(null);
            s_opcodes.Add(opcode.Value, opcode);
        }
    }

    public static bool ContainsOpcodes(MethodInfo methodInfo, IEnumerable<OpCode> targetOpCodes)
    {
        MethodBody methodBody = methodInfo.GetMethodBody();

        using (BinaryReader ilReader = new BinaryReader(new MemoryStream(methodBody.GetILAsByteArray())))
        {
            while (ilReader.BaseStream.Position < ilReader.BaseStream.Length)
            {
                short opCodeValue = ilReader.ReadByte();
                if (opCodeValue == 0xfe)
                    opCodeValue = (short)(opCodeValue << 8 | ilReader.ReadByte());

                OpCode opCode = s_opcodes[opCodeValue];
                if (targetOpCodes.Contains(opCode))
                    return true;

                int argumentSize = 4;
                if (opCode.OperandType == OperandType.InlineNone)
                    argumentSize = 0;
                else if (opCode.OperandType == OperandType.ShortInlineBrTarget || opCode.OperandType == OperandType.ShortInlineI || opCode.OperandType == OperandType.ShortInlineVar)
                    argumentSize = 1;
                else if (opCode.OperandType == OperandType.InlineVar)
                    argumentSize = 2;
                else if (opCode.OperandType == OperandType.InlineI8 || opCode.OperandType == OperandType.InlineR)
                    argumentSize = 8;
                else if (opCode.OperandType == OperandType.InlineSwitch)
                {
                    int num = ilReader.ReadInt32();
                    argumentSize = (int)(4 * num + 4);
                }

                ilReader.BaseStream.Position += argumentSize;
            }
        }

        return false;
    }
}

使用示例

private static void BoxingForEach()
{
    IEnumerable foo = (IEnumerable)new int[10];
    foreach (int i in foo) ;
}

private static void NoBoxingForEach()
{
    int[] foo = new int[10];
    foreach (int i in foo) ;
}

static void Main(string[] args)
{
    MethodInfo boxingForEach = typeof(Program).GetMethod("BoxingForEach", BindingFlags.Static | BindingFlags.NonPublic);
    MethodInfo noBoxingForEach = typeof(Program).GetMethod("NoBoxingForEach", BindingFlags.Static | BindingFlags.NonPublic);

    Console.WriteLine("BoxingForEach is using boxing: {0}", 
        ILUtils.ContainsOpcodes(boxingForEach, new[] { OpCodes.Box, OpCodes.Unbox, OpCodes.Unbox_Any }));

    Console.WriteLine("NoBoxingForEach is using boxing: {0}", 
        ILUtils.ContainsOpcodes(noBoxingForEach, new[] { OpCodes.Box, OpCodes.Unbox, OpCodes.Unbox_Any }));
}

结果

BoxingForEach is using boxing: True

NoBoxingForEach is using boxing: False