如何使用Reflection.Emit創建多維數組

Question

我想使用Reflection.Emit創建一個多維數組並設置它的元素。 像下面的C＃代碼一樣：

int[,] nums = new int[2, 2];
nums[1, 1] = 2;

轉入IL代碼：

IL_0000: nop
IL_0001: ldc.i4.2
IL_0002: ldc.i4.2
IL_0003: newobj instance void int32[0..., 0...]::.ctor(int32, int32)
IL_0008: stloc.0
IL_0009: ldloc.0
IL_000a: ldc.i4.1
IL_000b: ldc.i4.1
IL_000c: ldc.i4.2
IL_000d: call instance void int32[0..., 0...]::Set(int32, int32, int32)

用於創建數組的IL代碼：

newobj instance void int32[0..., 0...]::.ctor(int32, int32)

以及用於設置數組元素的IL代碼：

call instance void int32[0..., 0...]::Set(int32, int32, int32)

什么樣的IL Generator.Emit（）代碼對應那兩個IL句子？

Answer 1

你幾乎可以口頭翻譯那個IL：

il.Emit(OpCodes.Ldc_I4_2);
il.Emit(OpCodes.Ldc_I4_2);

var constructor = typeof(int[,]).GetConstructor(new Type[]{ typeof(int), typeof(int) });
il.Emit(OpCodes.Newobj, constructor);
il.Emit(OpCodes.Stloc_0);
il.Emit(OpCodes.Ldloc_0);
il.Emit(OpCodes.Ldc_I4_1);
il.Emit(OpCodes.Ldc_I4_1);
il.Emit(OpCodes.Ldc_I4_2);

var setMethod = typeof(int[,]).GetMethod("Set");
il.Emit(OpCodes.Call, setMethod);

當然，您需要使用反射來實際獲取Newobj和Call代碼所需的ConstructorInfo和MethodInfo對象。

Answer 2

這是一個例子：

DynamicMethod method =
    new DynamicMethod("Test" , typeof(int[,]), new Type[]{});

var generator = method.GetILGenerator();

//get the constructor that takes in 2 integers (the dimensions of the array)
var constructor = typeof (int[,])
    .GetConstructor(new {typeof (int), typeof (int)});

//get the Set method that takes in 3 integers; 2 indexes and the value 
var set_method = typeof(int[,])
    .GetMethod("Set", new[] { typeof(int), typeof(int), typeof(int) });

var local = generator.DeclareLocal(typeof (int[,])); //local variable to reference the array

generator.Emit(OpCodes.Ldc_I4_2);
generator.Emit(OpCodes.Ldc_I4_2);
generator.Emit(OpCodes.Newobj, constructor); //invoke the constructor to create the array
generator.Emit(OpCodes.Stloc, local);
generator.Emit(OpCodes.Ldloc, local);
generator.Emit(OpCodes.Ldc_I4_1);
generator.Emit(OpCodes.Ldc_I4_1);
generator.Emit(OpCodes.Ldc_I4_2);
generator.Emit(OpCodes.Call, set_method); //call the Set method to set the value
generator.Emit(OpCodes.Ldloc, local);
generator.Emit(OpCodes.Ret);

var result_method = (Func<int[,]>)method.CreateDelegate(typeof (Func<int[,]>));

var result = result_method(); //returns the array

此示例創建一個動態方法，用於創建數組，填充[1,1]中的值，然后返回該數組。