调用[myFunction]的结果未使用

In Obj-C, a common practice was to use convenience functions to perform common operations, like configuring auto layout for views:

在Obj-C中，常见的做法是使用便捷函数来执行常见操作，例如为视图配置自动布局：

func makeConstraint(withAnotherView : UIView) -> NSLayoutConstraint
{
   // Make some constraint 
   // ...

   // Return the created constraint
   return NSLayoutConstraint()
}

If you just needed to set the constraint and forget about it, you could call:

如果您只需要设置约束并忘记它，您可以调用：

[view1 makeConstraint: view2]

[view1 makeConstraint：view2]

If you wanted to store the constraint later so that you could remove/modify it, you would do something like:

如果您想稍后存储约束以便可以删除/修改它，您可以执行以下操作：

NSLayoutConstraint * c;
c = [view1 makeConstraint: view2]

I want to do this in swift, but if I call the above function and do not capture the returned constraint, I get the warning:

我想在swift中执行此操作，但如果我调用上面的函数并且不捕获返回的约束，我会收到警告：

Result of call to 'makeConstraint(withAnotherView:)' is unused

VERY annoying. Is there some way to let Swift know that I don't always want to capture the return value?

很烦人。有没有办法让Swift知道我并不总是想要捕获返回值？

NOTE: I know about this. It is ugly and not what I'm looking for:

注意：我知道这一点。这很难看，而不是我想要的：

_ = view1.makeConstraint(withAnotherView: view2)

2 个解决方案

#1

This is behaviour that has been introduced in Swift 3. Instead of having to explicitly annotate functions with @warn_unused_result in order to tell the compiler that the result should be used by the caller, this is now the default behaviour.

这是在Swift 3中引入的行为。为了告诉编译器调用者应该使用结果，不必使用@warn_unused_result显式地注释函数，现在这是默认行为。

You can use the @discardableResult attribute on your function in order to inform the compiler that the return value doesn't have to be 'consumed' by the caller.

您可以在函数上使用@discardableResult属性，以通知编译器返回值不必由调用者“消耗”。

@discardableResult
func makeConstraint(withAnotherView : UIView) -> NSLayoutConstraint {

   ... // do things that have side effects

   return NSLayoutConstraint()
}

view1.makeConstraint(view2) // No warning

let constraint = view1.makeConstraint(view2) // Works as expected

You can read about this change in more detail on the evolution proposal.

您可以在进化建议中更详细地了解此更改。

#2

You can try to turn the warnings off from the Build Settings of your project. I like the question, good point. Done some research and found this. https://*.com/a/34932152/5615274

您可以尝试从项目的“生成设置”中关闭警告。我喜欢这个问题，好点。做了一些研究，发现了这一点。 https://*.com/a/34932152/5615274

Did not test it yet.

还没测试过。

#1