Re: [boost] compact_optional -- prompting interest

Subject: Re: [boost] compact_optional -- prompting interest
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2015-09-29 04:16:04

2015-09-29 9:11 GMT+02:00 Gonzalo BG <gonzalobg88_at_[hidden]>:

>
>
> @Andrzej: Right now your implementation allows constructing a
> compact_optional from the sentinel value, which results in an empty
> compact_optional. What is the motivation for this?
>
> In my fork I've disabled it for the following reasons:
> - I'd rather use compact_optional's default constructor to explicitly state
> that i'm constructing an empty optional, this made it easier to reason
> about my code,
> - the other constructors from value_type can then hint the compiler that
> the compact_optional is not empty (but I did not profile so I don't know if
> this has any impact at all).
>

The motivation for this was to enable an integration of compact_optional
with older/other parts of the program that still use magical values:

```
using Index = compact_optional<evp_int<string::size_type, string::npos>>
string s = /*...*/
Index i {s.find("substr")};
```

In the above example, I will not be changing std, but want to change to
compact_optional as soon as possible.

But in fact, I could provide a dedicated conversion function for this use
case. This aspect is still under consideration, so I may go with your
suggestion.

Regards,
&rzej