c# - 为什么代码生成名为 <>c__DisplayClass1 的 MSIL 类

Question

我有这个代码，

private bool MatchingBreak(IEnumerable<CarriagewaySummary> breaks, int startMetres, int divisionPosition)
    {
        CarriagewaySummary matchingBreak = breaks.Where(x =>
        {
            return x.StartMetres == startMetres && x.EndMetres == divisionPosition;
        }).SingleOrDefault();
        return matchingBreak != null;
    }

为什么会在 MSIL 中生成一个名为 <>c__DisplayClass1 的嵌套类？

.class nested private auto ansi sealed beforefieldinit <>c__DisplayClass1
extends object
{
.custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
    01 00 00 00
)
// Fields
.field public int32 startMetres
.field public int32 divisionPosition

// Methods
.method public hidebysig specialname rtspecialname 
    instance void .ctor () cil managed 
{
    // Method begins at RVA 0x56fb
    // Code size 7 (0x7)
    .maxstack 8

    IL_0000: ldarg.0
    IL_0001: call instance void object::.ctor()
    IL_0006: ret
} // End of method <>c__DisplayClass1..ctor

.method public hidebysig 
    instance bool <MatchingBreak>b__0 (
        class TreatmentLengthDynamicSegmentation.Domain.CarriagewaySummary x
    ) cil managed 
{
    // Method begins at RVA 0x5704
    // Code size 37 (0x25)
    .maxstack 2
    .locals init (
        [0] bool 
    )

    IL_0000: nop
    IL_0001: ldarg.1
    IL_0002: callvirt instance int32 TreatmentLengthDynamicSegmentation.Domain.CarriagewaySummary::get_StartMetres()
    IL_0007: ldarg.0
    IL_0008: ldfld int32 class TreatmentLengthDynamicSegmentation.ScriptHelpers.DivisionManager/<>c__DisplayClass1::startMetres
    IL_000d: bne.un.s IL_001f
    IL_000f: ldarg.1
    IL_0010: callvirt instance int32 TreatmentLengthDynamicSegmentation.Domain.CarriagewaySummary::get_EndMetres()
    IL_0015: ldarg.0
    IL_0016: ldfld int32 class TreatmentLengthDynamicSegmentation.ScriptHelpers.DivisionManager/<>c__DisplayClass1::divisionPosition
    IL_001b: ceq
    IL_001d: br.s IL_0020
    IL_001f: ldc.i4.0
    IL_0020: stloc.0
    IL_0021: br.s IL_0023
    IL_0023: ldloc.0
    IL_0024: ret
} // End of method <>c__DisplayClass1.<MatchingBreak>b__0

} // End of class TreatmentLengthDynamicSegmentation.ScriptHelpers.DivisionManager/<>c__DisplayClass1

生成的代码干扰了 Nitriq 代码分析，所以我想了解它存在的原因。

Answer 1

如果你在 lambda 中使用局部变量，它需要在堆上。 lambda 可能会在创建它的函数退出后使用。正常的局部变量(存在于堆栈/寄存器中)在函数退出时变得无效，因此不能在这里使用。

因此，C# 编译器创建了一个类来保存捕获的局部变量。这就是您看到的那个。

请注意，C# 捕获的是实际变量，而不是其当前值。所以从概念上讲，它是通过引用捕获的。捕获的语义意味着编译器需要为每个作用域创建一个容器对象。

http://csharpindepth.com/Articles/Chapter5/Closures.aspx

---

在你的代码中

x =>
    {
        return x.StartMetres == startMetres && x.EndMetres == divisionPosition;
    }

lambda 使用 startMetres 和 divisionPosition，因此它们都被捕获并放入该嵌套类中。