当函数没有返回时，VB.NET 中没有警告 [英] No warning in VB.NET when function has no return

问题描述

一些评论堆栈溢出问题 为什么 C# 编译器不停止引用自身的属性? 关于警告让我想到了在我编写更多 VB.NET 代码时总是让我感到困惑的老问题.

Some comments on Stack Overflow question Why doesn't the C# compiler stop properties from referring to themselves? regarding warnings got me thinking about old issues that always goofed me up when I was writing more VB.NET code.

其中之一是编译器不会警告您是否声明了一个函数，但从未执行过显式的 Return 语句或分配给函数名称.运行 Visual Studio 2008，我刚刚做了一个小的实验项目，似乎这个行为从来没有被修复过.我创建了一个 Visual Basic 控制台应用程序，代码如下:

One of them was the fact that the compiler didn't warn if you declared a Function but never did an explicit Return statement or assign to the Function name. Running Visual Studio 2008, I just made a small experimental project, and it seems as though the behavior has never been fixed. I created a Visual Basic Console application, with the following code:

Module MainModule

    Sub Main()

        Dim test As Boolean = TestWarning()

    End Sub

    Function TestWarning() As Boolean

        Console.WriteLine("There is no Return Statement")

    End Function

End Module

我还进入了项目设置并打开了On Option Strict 和Option Explicit.我还设置了警告配置，以便没有返回值的函数/运算符".被设置为错误.

I also went into the Project Settings and turned On Option Strict and Option Explicit. I also set the Warning Configurations so that "Function/Operator with no return value" was set to Error.

我编译了项目，没有收到警告，TestWarning() 函数也没有错误.这似乎是放置警告的好地方，因为它默认为 False，而您可能只是忘记了返回.C# 将在没有 return 语句的情况下出错.我认为 VB.NET 对没有返回值的函数/运算符"做了同样的事情.配置.这是一个错误，还是我遗漏了什么?

I compiled the project and got no warning, and no error on the TestWarning() Function. This seems like a great place to put a warning, because it will default to False, and you may have simply forgotten to do a return. C# will error without a return statement. I thought that VB.NET did the same thing with the "Function/Operator with no return value" configuration. Is this a bug, or is there something I'm missing?

Function TestWarning() As Boolean

    If DateTime.Now.DayOfWeek = DayOfWeek.Monday Then
        Return False
    Else
        Console.WriteLine("There is no Return Statement")
    End If

End Function

如果我在 If 中有一个显式的 Return，而 Else 中没有任何内容，那么也不会出现警告或错误.它只会采用默认值，即使您可能打算(通过编程风格)获得显式返回.在这种情况下，我显式返回了 False(这是 Boolean 的默认值)，所以它可能是一个隐藏的错误，我应该在 Else<中返回 True/代码>.

If I have an explicit Return in an If, and nothing in the Else, there is also no warning or error. It will simply take the default, even though you likely intended (via programming style) to have an explicit return. In this case, I explicitly returned False (which is the default for Boolean), so it's likely a hidden bug that I should have returned True in the Else.

推荐答案

该警告只会在函数默认返回 Nothing 时通知您.

The warning will only let you know when a function is going to return Nothing by default.

如果返回值是引用类型，您会收到警告.

You would get a warning if return value was of a reference type.

但是你的函数有一个值类型的返回值，而那些不能是Nothing.因此，没有警告.

But your function has a return value of a value type, and those cannot be Nothing. Therefore, no warning.

这是因为这个函数内部的函数名充当结果变量.您可以通过将值分配给函数名称而不是使用 Return 来返回值.并且所有变量都使用默认值进行初始化，包括函数名变量.C 中不是这种情况，因此警告的含义不同.

This is because function name inside this very function acts as a result variable. You can return a value by assigning it to the function name instead of using Return. And all variables are initialized with default values, including the function-name variable. This is not the case in C, hence the different meaning of the warning.

将其与在初始化变量之前使用变量进行比较:

Compare this to using variables before initializing them:

Dim x As Integer
CallFunction(x)  'No warning, x is implicitly and properly initialized to 0.

Dim y as Object
CallFunction(y)  'A warning: variable used before a value is assigned to it

这篇关于当函数没有返回时，VB.NET 中没有警告的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！