C#表达式内部结构

我在努力理解表达是如何在课堂上起作用的

一个简单的例子：

Expression<Func<string, bool>> exp = p => p.Contains("x");

---

是微软魔术吗？我没有找到任何超调转换器或其他东西，谁调用了参数方法？他们是否在编译器中编写了一些特殊代码来编译Expression类而不是任何其他“标准”类？

是的，您可以称之为magic，因为编译器会在后台为您做很多提升。让我们看看最简单的程序会发生什么。我刚刚创建了一个控制台应用程序并添加了您的代码

internal class Program {
    private static void Main(string[] args) {
        Expression<Func<string, bool>> exp = p => p.Contains("x");
    }
}

内部类程序{
私有静态void Main（字符串[]args）{
表达式exp=p=>p.Contains（“x”）；
}
}

我编译了它并查看了IL代码。（如果您愿意，可以跳过此部分）

IL_0000:ldtoken[mscorlib/*23000001*/]System.String/*01000021*/
IL_0005:调用类[mscorlib/*23000001*/]System.Type/*01000014*/[mscorlib/*23000001*/]System.Type/*01000014*/：：GetTypeFromHandle（值类型[mscorlib/*23000001*/]System.RuntimeTypeHandle/*01000022*/）/*0A000014*/
IL_000a:ldstr“p”
IL_000f:调用类[System.Core/*23000002*/]System.Linq.Expressions.ParameterExpression/*0100001D*/[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/：：参数（类[mscorlib/*23000001*/]System.Type/*01000014*/，字符串）/*0A000040*/
IL_0014:stloc.0//V_0
IL_0015:ldloc.0//V_0
IL_0016:ldtoken方法实例bool[mscorlib/*23000001*/]System.String/*01000021*/：：Contains（String）/*0A000041*/
IL_001b:调用类[mscorlib/*23000001*/]System.Reflection.MethodBase/*0100002E*/[mscorlib/*23000001*/]System.Reflection.MethodBase/*0100002E*/：：GetMethodFromHandle（值类型[mscorlib/*23000001*/]System.RuntimeMethodHandle/*0100002F*/）/*0A000042*/
IL_0020:castclass[mscorlib/*23000001*/]System.Reflection.MethodInfo/*01000017*/
IL_0025:ldc.i4.1
IL_0026:newarr[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/
IL_002b:dup
IL_002c:ldc.i4.0
IL_002d:ldstr“x”
IL_0032:ldtoken[mscorlib/*23000001*/]System.String/*01000021*/
IL_0037:调用类[mscorlib/*23000001*/]System.Type/*01000014*/[mscorlib/*23000001*/]System.Type/*01000014*/：：GetTypeFromHandle（值类型[mscorlib/*23000001*/]System.RuntimeTypeHandle/*01000022*/）/*0A000014*/
IL_003c:调用类[System.Core/*23000002*/]System.Linq.Expressions.ConstantExpression/*01000030*/[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/：：常量（对象，类[mscorlib/*23000001*/]System.Type/*01000014*/）/*0A000043*/
IL_0041:stelem.ref
IL_0042:调用类[System.Core/*23000002*/]System.Linq.Expressions.MethodCallExpression/*01000031*/[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/：：调用（类[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/，类[mscorlib/*23000001*/]System.Reflection.MethodInfo/*01000017*/，类[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/[]）/*0A000044*/
IL_0047:ldc.i4.1
IL_0048:newarr[System.Core/*23000002*/]System.Linq.Expressions.ParameterExpression/*0100001D*/
IL_004d:dup
IL_004e:ldc.i4.0
IL_004f:ldloc.0//V_0
IL_0050:stelem.ref
IL_0051:调用类[System.Core/*23000002*/]System.Linq.Expressions.Expression`1/*01000032*/*/>[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/::Lambda（class[System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/，class[System.Core/*23000002*/]System.Linq.Expressions.ParameterExpression/*0100001D*/[]）/*2B00002*/
IL_0056：流行音乐

这个IL代码大致翻译为

// Define Expresin parameter p
var parameterExpression = Expression.Parameter(typeof (string), "p");
// Gets method handler for string.Contains method
// Plase note that __methodref can not be used in c# butit is valid in il code
var methodInfo = (MethodInfo) MethodBase.GetMethodFromHandle(__methodref (string.Contains));
// Constant string x added as paramter
var constantXString = new Expression[] {Expression.Constant("x", typeof (string))};
// Call given method on the the given parameter and make it into a lambda expression
Expression.Lambda<Func<string, bool>>(Expression.Call(parameterExpression, methodInfo, constantXString), parameterExpression);

//定义Expresin参数p
var parameterExpression=Expression.Parameter（typeof（string），“p”）；
//获取string.Contains方法的方法处理程序
//请注意，methodref不能在c中使用，但它在il代码中有效
var methodInfo=（methodInfo）MethodBase.GetMethodFromHandle（uuMethodRef（string.Contains））；
//常量字符串x添加为参数
var constantTXString=新表达式[]{Expression.Constant（“x”，typeof（string））}；
//对给定参数调用给定的方法，并将其转换为lambda表达式
Lambda（Expression.Call（parameterExpression、methodInfo、ConstantTXString）、parameterExpression）；

---

这是代码的第一行，您可以看到正在调用

公共静态参数expression Parameter（Type Type，string name）

。

NB。我已经编写了一个函数，它接受一个表达式树并生成一个字符串。@ZevSpitz NB您也可以。让我看看it@ZevSpitz很整洁！我喜欢

IL_0000: ldtoken      [mscorlib/*23000001*/]System.String/*01000021*/
IL_0005: call         class [mscorlib/*23000001*/]System.Type/*01000014*/ [mscorlib/*23000001*/]System.Type/*01000014*/::GetTypeFromHandle(valuetype [mscorlib/*23000001*/]System.RuntimeTypeHandle/*01000022*/)/*0A000014*/
IL_000a: ldstr        "p"
IL_000f: call         class [System.Core/*23000002*/]System.Linq.Expressions.ParameterExpression/*0100001D*/ [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/::Parameter(class [mscorlib/*23000001*/]System.Type/*01000014*/, string)/*0A000040*/
IL_0014: stloc.0      // V_0
IL_0015: ldloc.0      // V_0
IL_0016: ldtoken      method instance bool [mscorlib/*23000001*/]System.String/*01000021*/::Contains(string)/*0A000041*/
IL_001b: call         class [mscorlib/*23000001*/]System.Reflection.MethodBase/*0100002E*/ [mscorlib/*23000001*/]System.Reflection.MethodBase/*0100002E*/::GetMethodFromHandle(valuetype [mscorlib/*23000001*/]System.RuntimeMethodHandle/*0100002F*/)/*0A000042*/
IL_0020: castclass    [mscorlib/*23000001*/]System.Reflection.MethodInfo/*01000017*/
IL_0025: ldc.i4.1
IL_0026: newarr       [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/
IL_002b: dup
IL_002c: ldc.i4.0
IL_002d: ldstr        "x"
IL_0032: ldtoken      [mscorlib/*23000001*/]System.String/*01000021*/
IL_0037: call         class [mscorlib/*23000001*/]System.Type/*01000014*/ [mscorlib/*23000001*/]System.Type/*01000014*/::GetTypeFromHandle(valuetype [mscorlib/*23000001*/]System.RuntimeTypeHandle/*01000022*/)/*0A000014*/
IL_003c: call         class [System.Core/*23000002*/]System.Linq.Expressions.ConstantExpression/*01000030*/ [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/::Constant(object, class [mscorlib/*23000001*/]System.Type/*01000014*/)/*0A000043*/
IL_0041: stelem.ref
IL_0042: call         class [System.Core/*23000002*/]System.Linq.Expressions.MethodCallExpression/*01000031*/ [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/::Call(class [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/, class [mscorlib/*23000001*/]System.Reflection.MethodInfo/*01000017*/, class [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/[])/*0A000044*/
IL_0047: ldc.i4.1
IL_0048: newarr       [System.Core/*23000002*/]System.Linq.Expressions.ParameterExpression/*0100001D*/
IL_004d: dup
IL_004e: ldc.i4.0
IL_004f: ldloc.0      // V_0
IL_0050: stelem.ref
IL_0051: call         class [System.Core/*23000002*/]System.Linq.Expressions.Expression`1/*01000032*/<!!0/*class [mscorlib*//*23000001*//*]System.Func`2*//*01000012*//*<string, bool>*/> [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/::Lambda<class [mscorlib/*23000001*/]System.Func`2/*01000012*/<string, bool>>(class [System.Core/*23000002*/]System.Linq.Expressions.Expression/*0100002D*/, class [System.Core/*23000002*/]System.Linq.Expressions.ParameterExpression/*0100001D*/[])/*2B000002*/
IL_0056: pop

// Define Expresin parameter p
var parameterExpression = Expression.Parameter(typeof (string), "p");
// Gets method handler for string.Contains method
// Plase note that __methodref can not be used in c# butit is valid in il code
var methodInfo = (MethodInfo) MethodBase.GetMethodFromHandle(__methodref (string.Contains));
// Constant string x added as paramter
var constantXString = new Expression[] {Expression.Constant("x", typeof (string))};
// Call given method on the the given parameter and make it into a lambda expression
Expression.Lambda<Func<string, bool>>(Expression.Call(parameterExpression, methodInfo, constantXString), parameterExpression);