Source code for the Learn Rust by Building Real Applications course.
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License: MIT License
Source code for the Learn Rust by Building Real Applications course.
Hello.
After completing your Rust course, I try to improve QueryString
to handle "percent"-encoded keys and values, by using the urlencoding
crate. I figured I have to change QueryString
and Value
to store String
objects instead of &str
slices, so:
#[derive(Debug)]
pub struct QueryString {
data: HashMap<String, Value>,
}
#[derive(Debug)]
pub enum Value {
Single(String),
Multiple(Vec<String>),
}
Unfortunately, the urlencoding::decode()
functions returns Cow<str>
instead of normal String
or &str
๐คฏ
How do I "convert" the Cow<str>
into String
? Should it even be converted? Is the following helper function reasonable ???
use urlencoding::decode;
fn url_decode(str: &str) -> String {
match decode(str) {
Ok(decoded) => decoded.into_owned(), // <-- the best way to get String from Cow<str> ???
Err(_) => str.to_owned(),
}
}
...or better to store Cow<str>
instances in the Value
??? ๐
Another problem arises when key
and val
are of type String
now:
impl From<&str> for QueryString {
fn from(s: &str) -> Self {
let mut data = HashMap::new();
for sub_str in s.split('&').filter(|x| !x.is_empty()) {
let mut parts = sub_str.splitn(2, '=');
let key = parts.next().map(str::trim).map(url_decode).unwrap_or_default(); // <-- String
let val = parts.next().map(str::trim).map(url_decode).unwrap_or_default(); // <-- String
data.entry(key.to_owned())
.and_modify(|existing| match existing {
Value::Single(prev_val) => {
*existing = Value::Multiple(vec![prev_val.to_owned(), val]);
}
Value::Multiple(vec) => vec.push(val),
})
.or_insert(Value::Single(val)); // <-- ERROR: use of moved value: `val` โน๏ธ
}
QueryString { data }
}
}
The value val
gets moved into the closure (at and_modify()
), even though I don't use the move
keyword ๐ข
Is there any way to prevent that? Solution I have found is by using clone()
method:
let key = parts.next().map(str::trim).map(url_decode).unwrap_or_default();
let val = parts.next().map(str::trim).map(url_decode).unwrap_or_default();
data.entry(key.to_owned())
.and_modify(|existing| match existing {
Value::Single(prev_val) => {
*existing = Value::Multiple(vec![prev_val.to_owned(), val.clone()]); // <-- clone!
}
Value::Multiple(vec) => vec.push(val.clone()), // <-- clone!
})
.or_insert(Value::Single(val));
Is this a proper solution, or how do I go about this ???
It feels like there is an unnecessary clone in the and_modify()
branch now. That's because if we actually enter the and_modify()
branch, then the or_insert()
branch will never be entered โ and vice versa. But how do we solve it?
Best regards!
Hi,
by default, gdb does not pretty-print rust structures as on your videos. Can you add info in README.md
how to set it up?
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