Validate: add .unwrap()-like functions

[hinto-janai]

This adds .unwrap()-like functions:

• validate_or()
• validate_or_else()
• validate_or_default()

Notably, the last one is handy for me in situations where I don't care about errors, I just need a valid struct:

let tmp = read_users_config_file();

// I don't care about what the error was,
// I just want a valid `Config` after this point.
let config = tmp.validate_or_default(&());

/* do stuff with config */

The alternative before this was:

let tmp = read_users_config_file();

let config = match tmp.validate(&()) {
    Ok(_) => tmp,
    Err(_) => Default::default(),
};

/* do stuff with config */

This can get verbose if you're dealing with many validations.

---

Since none of these functions return errors, it's a waste to collect them, so validate_ok(), a function that early returns a bool on occurring an error instead of allocating+collecting them was implemented, but getting it to work with the derive macro... seemed difficult, so I left it out.

How it would have looked:

if data.validate_ok(&()) {
    println!("data is ok");
}

Current code:

// Looks similar but `validate()` under the
// hood may be allocating a bunch of errors
// to return (that we aren't using...!)
if data.validate(&()).is_ok() {
    println!("data is ok, but at what cost...?");
}

[jprochazk]

Hi and thanks for the PR!

Maybe I'm missing something, but can't you do this already with existing Result combinators? (unwrap_or, unwrap_or_else, unwrap_or_default)

let tmp = read_users_config_file();

// the `map` here is to convert `Result<(), Errors>` to `Result<T, Errors>`
let config = tmp.validate(&()).map(|_| tmp).unwrap_or(Default::default());
let config = tmp.validate(&()).map(|_| tmp).unwrap_or_else(|| Default::default());
let config = tmp.validate(&()).map(|_| tmp).unwrap_or_default();

/* do stuff with config */

I don't want to increase the surface area of the library if it's not absolutely necessary.

Since none of these functions return errors, it's a waste to collect them, so validate_ok(), a function that early returns a bool on occurring an error instead of allocating+collecting them was implemented, but getting it to work with the derive macro... seemed difficult, so I left it out.

I have plans to implement this in #1 :)

[hinto-janai]

Yes, you can already do this, but those chains are quite hard to read compared to:

let config = tmp.validate_or_default(&());

Patterns that appear often tend to receive more concise functions, but,

I don't want to increase the surface area of the library

this is understandable.