Refactor codebase to use std::optional instead of boost::optional

[SiarheiFedartsou]

Description

We migrated to C++17 and can start using std::optional from standard library instead of boost::optional.

The main problem here is Boost.Spirit library which doesn’t support std::optional(see #6429 (comment)).

[Kaushik-Iyer]

Can I try to work on this? Which part of the codebase should I be looking at?

[nilsnolde]

GSoC has an application process, which we will follow. We’ll make an announcement as soon as that starts.

[code-sparsh]

I might be able to work on this. Is it available?

[nilsnolde]

It is. Do you want to be assigned?

[97littleleaf11]

oops, I already have some progress on this issue

[97littleleaf11]

@nilsnolde sorry for my previous misguiding comment. @code-sparsh It's fine that you take this issue! I will find another issue to work on later. Actually I haven't dig into the Boost.Spirit yet.

[code-sparsh]

@97littleleaf11 Oh okay. If you already have some progress, it's fair that you take the issue because I haven't started yet.

Regarding the Boost.Spirit, I did some research on it. I think it would require some extra workarounds to be able to support std::optional. That might add some extra boilerplate to the code. I don't know if that's feasible or not, because I am just a beginner in this.

[97littleleaf11]

@code-sparsh Thanks for your information! Yeah, someone might add a boilerplate for std::optional like this boostorg/spirit#270 (comment) . Also need to check the correct overloading func. I haven't made it and found it's a little bit beyond my ability. It would be fine that you can take this.

[mugr1x]

Hello, I also have some progress on this issue. Can I submit a PR ?

[SiarheiFedartsou]

Hello, I also have some progress on this issue. Can I submit a PR ?

Sure, why not? :)

[mugr1x]

Now I found out that boost::spirit::x3 works well with std::optional (and has only minor modifications needed for working). However is it intentional that one implements a whole CSV parser instead of linking against something like libcsv3 ?
Anyway, I also want to apply for Google summer of code. I also think should talk to a potentional menter before.
@SiarheiFedartsou Can we possibly chat, you know about what exactly you need for the project idea and if it would be a good fit ?