Xcode build error when I add enum to generic class?

Question

Why do I get an error when I add enum to generic class:

class TestClass<T>{ 
    enum TestEnum {
        case test
    }  
}

Error:

1.  While type-checking 'ExampleTest' at /Users/xxx/xxx/xx/xx/ExampleTest.swift:11:1
<unknown>:0: error: unable to execute command: Segmentation fault: 11
<unknown>:0: error: swift frontend command failed due to signal (use -v to see invocation)
Command /Applications/Xcode6-Beta3 2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift failed with exit code 254

But I don't get an error when I do this :

class TestClass{ 
    enum TestEnum {
        case test
    }  
}

or this:

class TestClass<T>{ 
}

Your first two examples are exactly identical - is it possible you may have posted the same snippet twice? — weltraumpirat
– weltraumpirat, Commented Jul 22, 2014 at 23:18
Compiler bug with the combination of generic class and nested enum. File a bug report and de-nest the enumeration for now as a workaround. — Nate Cook
– Nate Cook, Commented Jul 23, 2014 at 1:42
@NateCook Yeah it looks like it, do you see the same behavior when compiling the code? If so, you could add your comment as an answer so I could accept it. — Jimmy
– Jimmy, Commented Jul 23, 2014 at 11:15

Community · Accepted Answer · 2017-05-23 11:54:57Z

20

You can't nest any type inside a generic one and vice versa. In other words, you can't do things like these for classes, structs, and enums:

class Outer<T> {
    class Inner { }
}

and

class Outer {
    class Inner<T> { }
}

and even

class Outer<T> {
    class Inner<T> { }
}

Apple folks explained the reason for the restriction:

It's an implementation limitation. We'll remove the restriction once our compiler and runtime are able to correctly handle types nested in generic contexts.

P.S. Sorry that I post the answer so late but the issue is still there (XCode 6.2).

There was a very similar question, by the way.

edited May 23, 2017 at 11:54

CommunityBot

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answered Mar 12, 2015 at 13:46

Pavel Vergeev

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1 Comment

Fabio Felici Over a year ago

Swift 3.1 and XCode 8.3.2 support this now

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