Question

我想在运行时检查对象是否是可选的String类型。为什么以下不能在我的命令行项目中编译？

var p:String?

if p is String {
    println("p is string")
}
else {
    println("p is not string")
}

构建错误：

Bitcast requires both operands to be pointer or neither
  %81 = bitcast i8* %80 to %SS, !dbg !131
Invalid operand types for ICmp instruction
  %82 = icmp ne %SS %81, null, !dbg !131
PHI nodes must have at least one entry.  If the block is dead, the PHI should be removed!
  %85 = phi i64 
PHI node operands are not the same type as the result!
  %84 = phi i8* [ %81, %73 ]
LLVM ERROR: Broken function found, compilation aborted!
Command /Applications/Xcode6-Beta2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift failed with exit code 1

Answer 1

首先必须为其分配值。像这样：

var p : Any?

p = "String"

if p is String {
    println("p is a String")
} else {
    println("p is something else")
}

Answer 2

首先，即使XCode不正确，XCode也不应该崩溃，因此我会向Apple提交错误报告。

但是你的代码确实没有意义。您将p设置为可选字符串，然后询问它是否为字符串。一个可选的String可以包含一个String或者nil，所以你最好只检查它是不是nil：

var p: String?

if p {
println("p is string")
}
else {
println("p is not string")
}

Swift - 无法使用实例检查进行编译

2 个答案: