为什么Awaiters（异步/等待）结构，而不是类？可类中使用？ [英] Why are Awaiters (async/await) structs and not classes? Can classes be used?

问题描述

为什么是awaiters（GetAwaiter - 使一个类awaitable）结构，而不是类。是否危害到使用类？

Why are the awaiters (GetAwaiter - to make a class awaitable) structs and not classes. Does it harm to use a class?

public struct ConfiguredTaskAwaiter : ICriticalNotifyCompletion:

<一个href="http://referencesource.microsoft.com/#mscorlib/system/runtime/compilerservices/TaskAwaiter.cs#b8626cdb2f1cbe65" rel="nofollow">http://referencesource.microsoft.com/#mscorlib/system/runtime/compilerservices/TaskAwaiter.cs#b8626cdb2f1cbe65

public struct YieldAwaiter : ICriticalNotifyCompletion:

<一个href="http://referencesource.microsoft.com/#mscorlib/system/runtime/compilerservices/YieldAwaitable.cs#1e1219f924e9e3b7" rel="nofollow">http://referencesource.microsoft.com/#mscorlib/system/runtime/compilerservices/YieldAwaitable.cs#1e1219f924e9e3b7

public struct TaskAwaiter<TResult> : ICriticalNotifyCompletion

<一个href="http://referencesource.microsoft.com/#mscorlib/system/runtime/compilerservices/TaskAwaiter.cs#2c48fb3bdfc69022" rel="nofollow">http://referencesource.microsoft.com/#mscorlib/system/runtime/compilerservices/TaskAwaiter.cs#2c48fb3bdfc69022

推荐答案

背后做的原因 awaitables A结构是为了避免不必要的堆分配，并尽量减少内存占用时，编译器创建的状态机在幕后。

The reason behind making awaitables a struct is to avoid unnecessary heap allocations and minimize the memory footprint when the compiler creates the state machine behind the scenes.

这是一个实现细节。对于awaitable是类型这是没有必要结构，而不是类。为了加强这一说法，尝试编译Roslyn的异步方法在调试模式下，你会看到状态机变成一个类，其中，作为编纂发布将导致结构。更多关于在<一个href="http://stackoverflow.com/questions/33871181/why-are-async-state-machines-classes-and-not-structs-in-roslyn?newsletter=1&nl$c$c=493396%7c7764">Why是异步状态机类（而不是结构）的罗斯林？

This is an implementation detail. It is not necessary for an awaitable to be of type struct and not a class. To strengthen this statement, try compiling an async method in Roslyn in Debug mode, and you'll see the state-machine turn into a class, where-as compiling in Release will result in a struct. More on that in Why are async state machines classes (and not structs) in Roslyn?

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