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Linq相关:

Linq是以下列方式编译:

  1. 首先,LINQ 查询表达式转换为方法调用:

    public static void Main() {     var query = db.Cars.Select<Car, Car>(c => c);     foreach (Car aCar in query)     {          Console.WriteLine(aCar.Name);     } } 
  2. 如果 db.Cars 的类型是 IEnumerable<Car> (即它的 LINQ,对象),然后 lambda 表达式变成了一个单独的方法:

    private Car lambda0(Car c) {     return c; } private Func<Car, Car> CachedAnonymousMethodDelegate1; public static void Main() {     if (CachedAnonymousMethodDelegate1 == null)         CachedAnonymousMethodDelegate1 = new Func<Car, Car>(lambda0);     var query = db.Cars.Select<Car, Car>(CachedAnonymousMethodDelegate1);     foreach // ... } 

    在现实中不调用该方法 lambda0 但东西喜欢 <Main>b__0 (在 Main 是包含方法的名称)。同样,缓存的委托实际上调用 CS$<>9__CachedAnonymousMethodDelegate1

    如果您正在使用 SQL LINQ 然后 db.Cars 类型将为 IQueryable<Car>,此步骤是非常不同。相反,它会到表达式目录树的 lambda 表达式:

    public static void Main() {     var parameter = Expression.Parameter(typeof(Car), "c");     var lambda = Expression.Lambda<Func<Car, Car>>(parameter, new ParameterExpression[] { parameter }));     var query = db.Cars.Select<Car, Car>(lambda);     foreach // ... } 
  3. foreach 循环变成一个 try/finally 块 (这是相同的两个):

    IEnumerator<Car> enumerator = null; try {     enumerator = query.GetEnumerator();     Car aCar;     while (enumerator.MoveNext())     {         aCar = enumerator.Current;         Console.WriteLine(aCar.Name);     } } finally {     if (enumerator != null)         ((IDisposable)enumerator).Dispose(); } 
  4. 最后,这是为 IL 编译预期的方式。以下是为 IEnumerable<Car>

    // Put db.Cars on the stack L_0016: ldloc.0  L_0017: callvirt instance !0 DatabaseContext::get_Cars()   // “if” starts here L_001c: ldsfld Func<Car, Car> Program::CachedAnonymousMethodDelegate1 L_0021: brtrue.s L_0034 L_0023: ldnull  L_0024: ldftn Car Program::lambda0(Car) L_002a: newobj instance void Func<Car, Car>::.ctor(object, native int) L_002f: stsfld Func<Car, Car> Program::CachedAnonymousMethodDelegate1   // Put the delegate for “c => c” on the stack L_0034: ldsfld Func<Car, Car> Program::CachedAnonymousMethodDelegate1   // Call to Enumerable.Select() L_0039: call IEnumerable<!!1> Enumerable::Select<Car, Car>(IEnumerable<!!0>, Func<!!0, !!1>) L_003e: stloc.1   // “try” block starts here L_003f: ldloc.1  L_0040: callvirt instance IEnumerator<!0> IEnumerable<Car>::GetEnumerator() L_0045: stloc.3   // “while” inside try block starts here L_0046: br.s L_005a L_0048: ldloc.3   // body of while starts here L_0049: callvirt instance !0 IEnumerator<Car>::get_Current() L_004e: stloc.2  L_004f: ldloc.2  L_0050: ldfld string Car::Name L_0055: call void Console::WriteLine(string) L_005a: ldloc.3   // while condition starts here L_005b: callvirt instance bool IEnumerator::MoveNext() L_0060: brtrue.s L_0048  // end of while L_0062: leave.s L_006e   // end of try   // “finally” block starts here L_0064: ldloc.3  L_0065: brfalse.s L_006d L_0067: ldloc.3  L_0068: callvirt instance void IDisposable::Dispose() L_006d: endfinally  

    已编译的代码,IQueryable<Car> 版本是按预期也。这里是重要的部分,有别于上述 (本地变量会有不同的偏移和名称现在,但让我们忽略的):

    // typeof(Car) L_0021: ldtoken Car L_0026: call Type Type::GetTypeFromHandle(RuntimeTypeHandle)   // Expression.Parameter(typeof(Car), "c") L_002b: ldstr "c" L_0030: call ParameterExpression Expression::Parameter(Type, string) L_0035: stloc.3    // Expression.Lambda(...) L_0036: ldloc.3  L_0037: ldc.i4.1           // var paramArray = new ParameterExpression[1] L_0038: newarr ParameterExpression L_003d: stloc.s paramArray L_003f: ldloc.s paramArray L_0041: ldc.i4.0                    // paramArray[0] = parameter; L_0042: ldloc.3  L_0043: stelem.ref  L_0044: ldloc.s paramArray L_0046: call Expression<!!0> Expression::Lambda<Func<Car, Car>>(Expression, ParameterExpression[])   // var query = Queryable.Select(...); L_004b: call IQueryable<!!1> Queryable::Select<Car, Car>(IQueryable<!!0>, Expression<Func<!!0, !!1>>) L_0050: stloc.1  
posted on 2013-02-06 14:49 墙头草 阅读(2319) 评论(0)  编辑  收藏

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