How can I access a swift convenience variable from objc in lldb?

Question

I'm trying to set some convenience variable in a swift context and to access it from a ObjC context.

(lldb) expression -l swift -- var $answerSwift = 42
(lldb) expression -o -l swift -- $answerSwift
42
(lldb) expression -o -l objc -- $answerSwift
error: use of undeclared identifier '$answerSwift'

The other way around works perfectly fine:

(lldb) expression -l objc -- int $answerObjc = 42
(lldb) expression -o -l swift -- $answerObjc
42

How can I move a value from the swift scope (?) to the objC scope?

Given that Swift globals aren't visible in ObjC even in normal code, I would not be surprised if this was totally impossible. (Adding @objc to the Swift expression doesn't even parse.) — jscs
– jscs, Commented Mar 8, 2019 at 18:58
Swift Int's are structs not classes. I don't think you can access swift structs in ObjC in compiled code, so you won't be able to in the debugger either. Objects could be made to work though I wouldn't be surprised if they don't work out of the box. — Jim Ingham
– Jim Ingham, Commented Mar 11, 2019 at 18:39
I used Ints because I hoped they would make a good, simple example. In my initial setup I was trying to access objects. — 343max
– 343max, Commented Mar 13, 2019 at 11:24

343max · Accepted Answer · 2019-03-24 12:25:16Z

It's possible to create a "temporary context" that will be evaluated and then passed in as a variable to the expression by putting it in backticks.

So this is going to work for breakpoints in swift code:

(lldb) expression -l swift -- var $answerSwift = 42
(lldb) expression -o -l objc -- `$answerSwift`
42

When I have a breakpoint in swift code I tried to set an objc var like this:

(lldb) expression -l objc -- id $label = (id)self.label
error: use of undeclared identifier 'self'

The objc context can't access the swift variable self, so it fails.

But when putting self.label in backticks to create the temporary swift context I can assign it to the objc variable:

(lldb) expression -l objc -- id $label = (id)`self.label`
(lldb) expression -l objc -O -- $label
<UILabel: 0x7f8030c03c40; frame = (44 44; 42 21); text = 'Label'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x6000019b35c0>>

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