How to pretty print table values (rather than references)?

[moon6969]

How can I pretty print a table with the shared references dereferenced?

local serpent = require("serpent")

local shared_table = { a = 'a' }
local main_table = { first = shared_table, second = shared_table }

print("*** line  ***")
print(serpent.line(main_table))

print("*** dump  ***")
print(serpent.dump(main_table))

actual output:

*** line  ***
{first = {a = "a"} --[[table: 0x0002ff00]], second = nil --[[ref]]} --[[table: 0x0002ff60]] --[[incomplete output with shared/self-references skipped]]
*** dump  ***
do local _={second={a="a"},first=nil};local __={};_.first=_.second;return _;end

desired output something like:

{first = {a = "a"}, second = {a = "a"}}

or even better if it could also still indicate which values are shared, perhaps like this...

{first = {a = "a"} --[[table: 0x0002ff00]], second = {a = "a"} --[[ref table: 0x0002ff00]]} --[[table: 0x0002ff60]]

Use case is to quickly see actual table values in one place in a log file.

[pkulchenko]

Right now there is no way to do this, because the multiple references are resolved internally. I've been thinking about adding an option to do what you are describing, but it's going to run into an issue of detecting and preventing circular references. I don't think it's appropriate to have an option that may hang (or make the app to run out of memory) in some (albeit rare) cases, so there still has to be a way to stop traversing multi-refs. It should be possible to detect, but it's not trivial and will likely affect performance of the main path as well (as it requires creation of additional (local) tables to keep track of recursive references).

[moon6969]

Thanks for reply. Consider this a +1 for your thinkings!

[pkulchenko]

Thanks. It just occurred to me that there is a hybrid option, when the library keeps track of how many times it has seen a specific element. You (as the user) can then specify a threshold, which, when exceeded, will generate a reference, but if not, will expand the element (maybe with added comment if it has already been seen). It puts the onus on the user to update the threshold (the default will be 1), but still better than not having it and may not require significant revamping of the module.

Would something like this work for your use case?

[moon6969]

Sounds very promising.
The current set of data has 10k+ --[[ref]] lines, but I don't know just now how many different source elements they point to.
I suspect the most commonly referenced source table would have a few 100s of references.