There are several approaches with this
- `value_parser(N..M)`: creates an i64 range
- `value_parser(value_parser!(u16).range(10..))`: creates an u16 range
that starts at 10
- `RangeI64ValueParser`: create whatever range you want
I was hoping to generalize `RangeI64ValueParser` for any source type,
not just i64, but ran into issues and decided to punt. I chose `i64` as
the source type as it seemed the most general and didn't run into
portability issues like `isize`.
This is a step towards #3199. All that is left is for the derive to use
this.
This identified a problem with the blanket implementations for
`TypedValueParser`: it only worked on function pointer types and not unnamed
function tupes. The user has to explicitly decay the function type to a
function pointer to opt-in, so I changed the blanket impl. The loss of
the `OsStr` impl shouldn't be too bad.
To set the type, we offer
- `ValueParser::<type>` short cuts for natively supported types
- `TypedValueParser` for fn pointers and custom implementations
- `value_parser!(T)` for specialized lookup of an implementation
(inspired by #2298)
The main motivation for `value_parser!` is to help with `clap_derive`s
implementation but it can also be convinient for end-users.
When reading, this replaces nearly all of our current `ArgMatches` getters with:
- `get_one`: like `value_of_t`
- `get_many`: like `values_of_t`
It also adds a `get_raw` that allows accessing the `OsStr`s without
panicing.
The naming is to invoke the idea of a more general container which I
want to move this to.
The return type is a bit complicated so that
- Users choose whether to panic on invalid types so they can do their
own querying, like `get_raw`
- Users can choose how to handle not present easily (#2505)
We had to defer setting the `value_parser` on external subcommands,
for consistency sake, because `Command` requires `PartialEq` and
`ValueParser` does not impl that trait. It'll have to wait until a
breaking change.
Fixes#2505
