Crate inlinable_string [] [src]

The inlinable_string crate provides the InlinableString type — an owned, grow-able UTF-8 string that stores small strings inline and avoids heap-allocation — and the StringExt trait which abstracts string operations over both std::string::String and InlinableString (or even your own custom string type).

StringExt's API is mostly identical to std::string::String; unstable and deprecated methods are not included. A StringExt implementation is provided for both std::string::String and InlinableString. This enables InlinableString to generally work as a drop-in replacement for std::string::String and &StringExt to work with references to either type.


use inlinable_string::{InlinableString, StringExt};

// Small strings are stored inline and don't perform heap-allocation.
let mut s = InlinableString::from("small");
assert_eq!(s.capacity(), inlinable_string::INLINE_STRING_CAPACITY);

// Inline strings are transparently promoted to heap-allocated strings when
// they grow too big.
s.push_str("a really long string that's bigger than `INLINE_STRING_CAPACITY`");
assert!(s.capacity() > inlinable_string::INLINE_STRING_CAPACITY);

// This method can work on strings potentially stored inline on the stack,
// on the heap, or plain old `std::string::String`s!
fn takes_a_string_reference(string: &mut StringExt) {
   // Do something with the string...
   string.push_str("it works!");

let mut s1 = String::from("this is a plain std::string::String");
let mut s2 = InlinableString::from("inline");

// Both work!
takes_a_string_reference(&mut s1);
takes_a_string_reference(&mut s2);

Porting Your Code

  • If my_string is always on the stack: let my_string = String::new();let my_string = InlinableString::new();

  • fn foo(string: &mut String) { ... }fn foo(string: &mut StringExt) { ... }

  • fn foo(string: &str) { ... } does not need to be modified.

  • struct S { member: String } is a little trickier. If S is always stack allocated, it probably makes sense to make member be of type InlinableString. If S is heap-allocated and member is always small, consider using the more restrictive InlineString type. If member is not always small, then it should probably be left as a String.


InlinableString implements serde's Serialize and Deserialize traits. Add the serde feature to your Cargo.toml to enable serialization.


pub use inline_string::INLINE_STRING_CAPACITY;
pub use inline_string::InlineString;
pub use string_ext::StringExt;



A short UTF-8 string that uses inline storage and does no heap allocation. It may be no longer than INLINE_STRING_CAPACITY bytes long.


A trait that exists to abstract string operations over any number of concrete string type implementations.



An owned, grow-able UTF-8 string that allocates short strings inline on the stack.