How do I convert between String, &str, Vec<u8> and &[u8]?
A new Rustacean like me struggles with juggling these types: String
, &str
, Vec<u8>
, &[u8]
.
In time, I hope to have an epiphany and suddenly get why some library calls use one or the other. Until then, I need help to map out each idiomatic transition.
Given these types:
let st: &str = ...;
let s: String = ...;
let u: &[u8] = ...;
let v: Vec<u8> = ...;
I think I have figured these out, but are they idiomatic?
&str -> String String::from(st)
&str -> &[u8] st.as_bytes()
String -> &str s.as_str()
&[u8] -> &str str::from_utf8(u)
Vec<u8> -> String String::from_utf8(v)
Ultimately I want a complete table of transitions for these types:
&str -> String
&str -> &[u8]
&str -> Vec<u8>
String -> &str
String -> &[u8]
String -> Vec<u8>
&[u8] -> &str
&[u8] -> String
&[u8] -> Vec<u8>
Vec<u8> -> &str
Vec<u8> -> String
Vec<u8> -> &[u8]
Solution 1:
From &str
-
&str -> String
has many equally valid methods:String::from(st)
,st.to_string()
,st.to_owned()
.- But I suggest you stick with one of them within a single project. The major advantage of
String::from
is that you can use it as an argument to amap
method. So instead ofx.map(|s| String::from(s))
you can often usex.map(String::from)
.
- But I suggest you stick with one of them within a single project. The major advantage of
-
&str
->&[u8]
is done byst.as_bytes()
-
&str
->Vec<u8>
is a combination of&str -> &[u8] -> Vec<u8>
, i.e.st.as_bytes().to_vec()
orst.as_bytes().to_owned()
From String
-
String -> &str
should just be&s
where coercion is available ors.as_str()
where it is not. -
String -> &[u8]
is the same as&str -> &[u8]
:s.as_bytes()
-
String -> Vec<u8>
has a custom method:s.into_bytes()
From &[u8]
-
&[u8] -> Vec<u8>
is done byu.to_owned()
oru.to_vec()
. They do the same thing, butto_vec
has the slight advantage of being unambiguous about the type it returns. -
&[u8] -> &str
doesn't actually exist, that would be&[u8] -> Result<&str, Error>
, provided viastr::from_utf8(u)
-
str::from_utf8(u).unwrap()
works, but you should prefer better error handling (see Error handling - The Result type).
-
-
&[u8] -> String
is the combination of&[u8] -> Result<&str, Error> -> Result<String, Error>
-
String::from_utf8(u).unwrap()
works, but prefer better error handling (see Error handling - The Result type and alsoResult::map
.
-
From Vec<u8>
-
Vec<u8> -> &[u8]
should be just&v
where coercion is available, oras_slice
where it's not. -
Vec<u8> -> &str
is the same asVec<u8> -> &[u8] -> Result<&str, Error>
i.e.str::from_utf8(&v)
-
str::from_utf8(&v).unwrap()
works, but prefer better error handling (see Error handling - The Result type)
-
-
Vec<u8> -> String
doesn't actually exist, that would beVec<u8> -> Result<String, Error>
viaString::from_utf8(v)
-
String::from_utf8(v).unwrap()
works, but prefer better error handling (see Error handling - The Result type).
-
Coercion is available whenever the target is not generic but explicitly typed as &str
or &[u8]
, respectively. The Rustonomicon has a chapter on coercions with more details about coercion sites.
tl;dr
&str -> String | String::from(s) or s.to_string() or s.to_owned()
&str -> &[u8] | s.as_bytes()
&str -> Vec<u8> | s.as_bytes().to_vec() or s.as_bytes().to_owned()
String -> &str | &s if possible* else s.as_str()
String -> &[u8] | s.as_bytes()
String -> Vec<u8> | s.into_bytes()
&[u8] -> &str | s.to_vec() or s.to_owned()
&[u8] -> String | std::str::from_utf8(s).unwrap(), but don't**
&[u8] -> Vec<u8> | String::from_utf8(s).unwrap(), but don't**
Vec<u8> -> &str | &s if possible* else s.as_slice()
Vec<u8> -> String | std::str::from_utf8(&s).unwrap(), but don't**
Vec<u8> -> &[u8] | String::from_utf8(s).unwrap(), but don't**
* target should have explicit type (i.e., checker can't infer that)
** handle the error properly instead