Array of different lifetime element to array of cow

help
1

I need to return a list of Cow<str> from a function, but my strs have different lifetimes. Before they had different lifetime, I could just map to Cow::from, but now I need to specify for each element:

        [
            Cow::from(format!("{}", self.id)),
            Cow::from(amount_string),
            Cow::from(self.description.to_string()),
            Cow::from(self.receiver.to_string()),
            Cow::from(format!("{}", self.date.format("%v %H:%M"))),
            Cow::Borrowed(&self.account.name),
            Cow::from(acc_string),
        ]
        .into_iter()
        // .map(Cow::from)
        .collect()

Is there a way for the map to know when to Borrow and when to take ownership ?
Thank you

2

You can't have both Strings and &strs in the array (or iterate over more than one type either).

3

Could you clarify what you're trying to accomplish? You already have an array of Cows and from it you create an iterator of Cows and collect it into a collection (say, Vec<Cow<str>>). So why do you want to use map(Cow::from)? What do you want to do that's different from, say:

vec![
    Cow::from(format!("{}", self.id)),
    Cow::from(amount_string),
    Cow::from(self.description.to_string()),
    Cow::from(self.receiver.to_string()),
    Cow::from(format!("{}", self.date.format("%v %H:%M"))),
    Cow::Borrowed(&self.account.name),
    Cow::from(acc_string),
]

?

4

If the type of the resulting vector is explicitly annotated as Vec<Cow<'_, str>>, then you can replace all the Cow::from()s with .into()s:

let list: Vec<Cow<'_, str>> = vec![
    format!("{}", self.id).into(),
    amount_string.into(),
    self.description.to_string().into(),
    self.receiver.to_string().into(),
    format!("{}", self.date.format("%v %H:%M")).into(),
    (&self.account.name).into(),
    acc_string.into(),
];
1 Like
5

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