出现原因:

在使用Xcode中新建playground界面直接报错
报错原因如下:

Unable to find execution service for selected run destination

解决办法:

1. 关闭xcode -> Command+Q
2. 打开终端,执行下列两行代码

rm -rf ~/Library/Developer/CoreSimulator/Devices
killall -9 com.apple.CoreSimulator.CoreSimulatorService