How to make string concatenation and convert `i128` to `String` and vice versa

[jaunty silo]

Hi guys
Appreciate your help. How can I cancate two strings? and how can I convert from string and to string ? It seems that rust native ways are not supported .
Thank you

[rigid obsidian]

you can do that with rust, but you need to enable alloc to use String, which both increases the contract size and makes it slower/more expensive. so if you can avoid that, you probably should

https://soroban.stellar.org/docs/basic-tutorials/alloc