Borrow checker saying stuff I don't understand.

[open edge]

I'm trying to implement a simple calculator Lexer(just trying, dunno how I'm gonna parse it).
While doing it, the borrow checker is boring me... a lot. In the code below, it complains about something like "creating tempory value", when I created nothing, I'm just using native code. ```rs
let value = match self {
Sign::PlusSign => "+",
Sign::MinusSign => "-",
Sign::MultiplicationSign => "*",
Sign::DivisionSign => "/",
Sign::Number(value) => value.to_string().as_str(),
};

    String::from(value)

I solved that by calling `String::from` in every match, but I don't understand why it doesn't work. What I solved with:rs
let value = match self {
Sign::PlusSign => String::from("+"),
Sign::MinusSign => String::from("-"),
Sign::MultiplicationSign => String::from("*"),
Sign::DivisionSign => String::from("/"),
Sign::Number(value) => value.to_string(),
};

    value

``` PS: Sign::Number holds an i32

[edgy tiger]

I created nothing,
the thing created is value.to_string()

that is a newly-allocated string

[open edge]

?

But it's a method in the core, I didn't do anything.

[edgy tiger]

you called to_string(), which returns a String value

then you called as_str() on it, which borrows that String

but then the string is dropped, by exiting that scope, before the borrow (value) is used

you need to avoid doing that

which you did by using String instead of &str in the match

[open edge]

I didn't understand anything, lol.

[open edge]

Isn't it just sent to the variable, like let hello = "hello"

basically the same thing..

[edgy tiger]

as_str() borrows the String it's called on

as_str() returns the borrow, not the string

the problem is that the String didn't get stored in any variable

[open edge]

so I have to do a block? wot..

[edgy tiger]

in this situation you can't (or well, can't directly)

your second code block is one correct way to handle this problem

there are ways to make it a little more concise, though

[open edge]

let smth = match self {
  Sign::Number(value) => {
    let string_value = value.to_string();

    string_value.as_str()
  }
}```Like that?

Like, this is confusing, lol

[edgy tiger]

no, that does not help because string_value is out of scope before the match finishes

there is a way to use a variable to extend it

[open edge]

?

what do I do them

cause I don't want to repeat String::from everytime.

[edgy tiger]

you can do this:

let tmp_str;
let value = match self {
    Sign::PlusSign => "+",
    Sign::MinusSign => "-",
    Sign::MultiplicationSign => "*",
    Sign::DivisionSign => "/",
    Sign::Number(value) => {
        tmp_str = value.to_string();
        tmp_str.as_str()
    }
};

String::from(value)

this is a bit of an odd technique but it does work when you just need to make one temporary value live longer

however, this isn't a great solution to the bigger problem

because you're allocating a string and then copying it into a second string (the String::from(value))

[open edge]

not my fault.

i32's fault

[edgy tiger]

here's how to make the match with conversion less busy:

match self {
    Sign::PlusSign => "+".into(),
    Sign::MinusSign => "-".into(),
    Sign::MultiplicationSign => "*".into(),
    Sign::DivisionSign => "/".into(),
    Sign::Number(value) => value.to_string(),
}

[open edge]

for not having as_str or something

[open edge]

Kinda same thing, but okay

[edgy tiger]

it's not possible for i32 to have an as_str, because as_str() is "give me a reference to the characters that are already in memory" and an i32 is not made of characters

[open edge]

it could do .to_string().as_str() in back, dunno.

anyways, now I have to think a way to parse stuff... somehow.

cause I dunno how to do it

[edgy tiger]

that's just as impossible for std as it is for your code

[edgy tiger]

let number: i32 = some_string.parse().expect("invalid number");

[open edge]

parse stuff = lexer parsing

pub enum Sign {
    PlusSign,
    MinusSign,
    MultiplicationSign,
    DivisionSign,
    Number(i32),
}```this kind of parsing.

[edgy tiger]

ah, I have no advice there as I haven't tackled that problem yet for myself

[open edge]

and I literally dunno how to do it

[edgy tiger]

I know there are libs for parsing but I haven't tried any

[open edge]

I'm not redoing this...

Anyways, I'm probably giving up on it, but thx for answering.

Cause I don't think I'll be able to parse those.