给出以下Swift代码,保存在bug.swift中,并使用Xcode 8.2.1或Xcode 8.3 beta 2:
import Foundation
protocol MyProtocol {
func foo() -> String
}
extension MyProtocol {
func foo() -> String {
return "\(self)"
}
}
extension String: MyProtocol {}
extension NSAttributedString: MyProtocol {}
let normal = "normal".foo()
let attributed = NSAttributedString(string: "attributed", attributes: [:]).foo()
运行以下命令:
swiftc -g bug.swift
lldb bug
LLDB启动.现在,运行这些命令,并观察输出.我通过的地方9,传递bug.swift包含的内容return "\(self)":
(lldb) target create "bug"
Current executable set to 'bug' (x86_64).
(lldb) b 9
Breakpoint 1: where = bug`(extension in bug):bug.MyProtocol.foo () -> Swift.String + 19 at bug.swift:9, address = 0x0000000100001e53
(lldb) run
Process 16370 launched: '/Users/zev/Desktop/bug' (x86_64)
Process 16370 stopped
* thread #1: tid = 0x31730e, 0x0000000100001e53 bug`MyProtocol.foo(self="normal") -> String + 19 at bug.swift:9, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000100001e53 bug`MyProtocol.foo(self="normal") -> String + 19 at bug.swift:9
6
7 extension MyProtocol {
8 func foo() -> String {
-> 9 return "\(self)"
10 }
11 }
12
(lldb) po self
"normal"
(lldb) c
Process 16370 resuming
Process 16370 stopped
* thread #1: tid = 0x31730e, 0x0000000100001e53 bug`MyProtocol.foo(self=0x00007fff5fbff480) -> String + 19 at bug.swift:9, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000100001e53 bug`MyProtocol.foo(self=0x00007fff5fbff480) -> String + 19 at bug.swift:9
6
7 extension MyProtocol {
8 func foo() -> String {
-> 9 return "\(self)"
10 }
11 }
12
(lldb) po self
error: <EXPR>:1:11: error: use of undeclared type '$__lldb_context'
extension $__lldb_context {
^~~~~~~~~~~~~~~
error: <EXPR>:18:5: error: use of unresolved identifier '$__lldb_injected_self'
$__lldb_injected_self.$__lldb_wrapped_expr_2(
^~~~~~~~~~~~~~~~~~~~~
我们第一次达到断点,我们String符合MyProtocol,我们可以成功po self.
然而,我们第二次达到断点时,我们NSAttributedString符合要求MyProtocol,并且LLDB打印出乱码而不是预期的输出po self.
为什么LLDB有时无法打印任何有用的内容？这是一个人为的例子,但我在LLDB的日常使用中一直遇到这种情况.