CODEWITHSUNDEEP
swiftxcodedebugginglldb
Jacek Lampart
Jacek Lampart

Reputation: 1751

Xcode lldb error: can't print out Swift variable - get "$__lldb_injected_self.$__lldb_wrapped_expr_x" instead

Sometimes, when trying to print out a variable in the debugger, the following error message is displayed:

error: warning: <EXPR>:12:9: warning: initialization of variable '$__lldb_error_result' was never used; consider replacing with assignment to '_' or removing it
    var $__lldb_error_result = __lldb_tmp_error
    ~~~~^~~~~~~~~~~~~~~~~~~~
    _

error: <EXPR>:18:5: error: use of unresolved identifier '$__lldb_injected_self'
    $__lldb_injected_self.$__lldb_wrapped_expr_120(     
    ^~~~~~~~~~~~~~~~~~~~~

This is a known lldb bug (https://bugs.swift.org/browse/SR-6156), but perhaps someone knows a workaround that can be used until that bug is fixed?

Upvotes: 17

Views: 8425

Answers (1)

Kamil.S
Kamil.S

Reputation: 5543

As a workaround you can print it in the lldb debugger using:

frame variable variablename

Also possible using shortened syntax for quicker typing

fr v variablename

Since XCode 10.2 an ever simpler lldb syntax is supported:

v variable

Update - new workarounds:

Print stack addresses:

v -L variablename

po like on stack frame variable.property

 v -o variablename.property

Swift like p

e unsafeBitCast(address, to: ClassName.self)

Update2 - new workaround applicable for Swift classes being wrappers of objc classes.

Example:

v response
(HTTPURLResponse) response = 0x0000000283ba7640 {

if v works^:

e -l objc -- (int)[0x0000000283ba7640 statusCode]
(int) $2 = 404

Update 3 printing Swift arrays (here array of [Int])

v -L arrayName
0x00007ff7b753a9a8: ([Int]) arrayName = 1169 values {
0x000060000295e7b0:   [0] = 1
...

then

e unsafeBitCast(0x00007ff7b753a9a8, to: UnsafeMutablePointer<Array<Int>>.self).pointee[0].bitWidth

also possible with map

e unsafeBitCast(0x00007ff7b753a9a8, to: UnsafeMutablePointer<Array<Int>>.self).pointee.map{ $0.bitWidth }

I'd appreciate reports what is actually helpful and works. Thanks.

More information on this kind of capabilities can be found here: https://developer.apple.com/library/content/documentation/General/Conceptual/lldb-guide/chapters/C5-Examining-The-Call-Stack.html

Upvotes: 42

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