Article about prefix dictionaries

[ProgramCrafter]

Summary

I'd like to see an article describing how to use prefix dictionaries in FunC. If TVM doesn't work correctly with regards to that functionality, I'd like a bug filed.

Context

It seems impossible to use those dictionaries correctly, but they may be quite useful for gas optimization. For instance, @Gusarich, in a discussion related to subdomains, reported:

strange, but zero byte in the end doesn't help. likely I have a bug somewhere.

I can store "test\0", and then I'm also able to store "testA\0", but if I try to append "testAB\0" as well, then pfxdict_get starts raising errors

and it doesn't just return flag 0 altogether; it raises error (9: error while parsing a dictionary node label)

Learning goals

Usage of prefix dictionaries on FunC and offchain sides, their applications to storing dictionaries like subdomains and

References

• https://docs.ton.org/develop/data-formats/tl-b-types#pfxhashmap
• https://docs.ton.org/develop/func/cookbook#how-to-iterate-dictionaries

Estimate suggested reward

1. TON Standard Footstep NFT
2. $600 in TON

Completion criteria

• [x] Article written
• [x] Article tested, bug reported if appropriate
• [ ] Bug resolved if it is there
• [x] Article published on docs.ton.org

[ProgramCrafter]

I'm ready to work on this footstep.