Impls of TryFrom

[Kixunil]

Here are some impls if TryFrom that I'd like to see. I checked against the documentation, not current git master. I'm sorry, if some are already resolved.

• TryFrom<&str> for numeric types (parsing)
• TryFrom<String> for numeric types (the benefit of this is that if you generically bound by TryFrom<String>, you may save allocation in case of TryFrom<String> for String
• TryFrom<OsStr> for numeric types (useful for parsing args_os or env_os)
• TryFrom<OsString> for numeric types
• all above combinations for IP addresses
• probably many more I don't remember right now

[SimonSapin]

I was wondering whether these could be based on FromStr, but unfortunately trait coherence doesn’t allow it:

error[E0119]: conflicting implementations of trait `convert::TryFrom<&str>`:
   --> libcore/convert.rs:430:1
    |
421 | impl<T, U> TryFrom<U> for T where T: From<U> {
    | -------------------------------------------- first implementation here
...
430 | impl<'a, T> TryFrom<&'a str> for T where T: ::str::FromStr {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation

error: aborting due to previous error

Maybe something something specialization something.

[Kixunil]

Yeah, I specifically listed them separately. I know that TryFrom was previously implemented in terms of FromStr but that was later changed.

[Mark-Simulacrum]

I am personally against seeing the parsing functions implemented via TryFrom, parsing seems like too specific a desire to be met with such a generic trait as TryFrom.

I think refiling this as specific issues for each impl (or at least, group of impls) is then the right way to move forward here, though I'd personally be against all the impls suggested here. Closing in favor of specific issues (which can then be decided on individually).

[Kixunil]

While I don't see the reason (FromStr was previously supposed to be deprecated in favor of TryFrom!), I don't really care anymore as I made a crate for my specific use case.