Expand description
§slimvec
§Overview
SlimVec is a dynamic-array containing a generic element type, mirroring the
api of the Standard Library’s Vec with a smaller inline stack size.
SlimVec stores its length & capacity alongside the buffer on the heap, as
illustrated:
SlimVec<T> Allocation
+-------------+ +-------------+
| ptr: 0xabcd | ----> | length: 2 |
+-------------+ |-------------|
| capacity: 4 |
|=============|
| 0: A |
|-------------|
| 1: B |
|-------------|
| 2: <uninit> |
|-------------|
| 3: <uninit> |
+-------------+An empty SlimVec may be created using SlimVec::new(), and like Vec it
will not allocate until elements are inserted or capacity is explicity
reserved. SlimVec::new is also a const fn.
use slimvec::SlimVec;
let mut v = SlimVec::new(); // Has not allocated yet
v.push(8); // Allocates when pushing the first elementThe slimvec! macro may be used to create & populate a SlimVec using the
same syntax as the Standard Library’s vec! macro:
use slimvec::slimvec;
slimvec![1f32; 5];
slimvec![1usize, 2, 3, 4, 5];SlimVec<T> dereferences to [T], so all slice methods are freely available.
This includes utilities such as sorting, searching, and iteration.
slimvec support no_std environments but alloc is required.
§Features
The slimvec package includes the following cargo-features:
§std
Enables std::io::Write for SlimVec<u8>.
§arbitrary
Enables support for arbitrary.
§serde
Enable serialisation and deserialisation via serde.
§Architecture
§Preamble
Dynamic arrays are composed of two main parts; the buffer - to contain its elements; and the length & capacity - respectively tracking the current number of elements, and maximum number of elements that may be stored before needing to reallocate. The buffer is placed in dynamically allocated heap-memory, and the owner holds onto a pointer to this memory.
§Vec
The Standard Library’s Vec uses its allocated heap-memory solely for the
buffer of elements. Inline it stores three values; the pointer to the buffer,
the length, & the capacity. This results in an inline-size for each Vec
equivalent to three usizes as depicted:
Vec<T> Allocation
+-------------+ +-------------+
| ptr: 0xabcd | ----> | 0: A |
|-------------| |-------------|
| length: 2 | | 1: B |
|-------------| |-------------|
| capacity: 4 | | 2: <uninit> |
+-------------+ |-------------|
| 3: <uninit> |
+-------------+§Motivations
The choices that the Standard Library’s Vec makes are great in the general
case. However there are some circumstances where it may possibly be suboptimal.
This library endeavors to provide an alternative structure for dynamic-arrays with a reduced inline-size, in order to mitigate this cost when the trade-off for doing so may be beneficial.
§As building blocks
Dynamic-arrays are often used as mere building-blocks of more complex data-structures. The inline-size of such data-structures may end up fairly large when they are composed of multiple collections.
This larger inline-size is a little bit more expensive to store and move around on the stack, which in some ways is slightly at odds with idiomatic Rust which tends to use the stack a lot.
§As user-data
At times certain kinds of libraries (physics-engines, graphics-APIs,
frameworks, &c.) will provide the application with the ability to associate a
small amount of data, often referred to as “user-data”, with an entity or
object otherwise managed by the library; frequently this user-data is large
enough to store only a mere usize.
If the application needs to store more data than it can encode in the limited
bits, then it may store in the user-data a pointer to the actual larger data.
Applications that want to use the user-data to associate a Vec<T> would in
fact have to store a Box<Vec<T>>, since the Standard Library’s Vec is too
large. This bestows an unfortunate double-indirection when accessing the
elements of the Vec.
§SlimVec
SlimVec stores its length & capacity alongside the buffer on the heap, as
illustrated:
SlimVec<T> Allocation
+-------------+ +-------------+
| ptr: 0xabcd | ----> | length: 2 |
+-------------+ |-------------|
| capacity: 4 |
|=============|
| 0: A |
|-------------|
| 1: B |
|-------------|
| 2: <uninit> |
|-------------|
| 3: <uninit> |
+-------------+This means the inline-size of a SlimVec is just a single pointer:
assert!(size_of::<SlimVec<T>>() == size_of::<usize>());SlimVec’s inline-data contains a niche, so that Option-like enums
containing a SlimVec have the same size:
assert!(size_of::<SlimVec<T>>() == size_of::<Option<SlimVec<T>>>());SlimVec includes a specialisation for the case that its elements are
Zero-Sized-Types (ZSTs), such that it need never allocate. In this special case
the length is stored inline.
Otherwise for regular (non-ZST) elements, a SlimVec contains a non-null
pointer to its memory-allocation, or a special sentinel-value when the
SlimVec has a capacity of zero.
The trade-off is that accessing the length or capacity may be more expensive as it requires dereferencing the pointer. In return the length & capacity need not be lugged around by the owner.
§Licensing
This library may be licensed under any of the following LICENSE-MIT, LICENSE-ZLIB, or LICENSE-APACHE2 at your option.
§LICENSE-MIT
Copyright © ickk, 2026
Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
§LICENSE-ZLIB
Copyright © ickk, 2026
This software is provided 'as-is', without any express or implied warranty. In
no event will the authors be held liable for any damages arising from the use
of this software.
Permission is granted to anyone to use this software for any purpose, including
commercial applications, and to alter it and redistribute it freely, subject to
the following restrictions:
1. The origin of this software must not be misrepresented; you must not claim
that you wrote the original software. If you use this software in a product,
an acknowledgment in the product documentation would be appreciated but is
not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
§LICENSE-APACHE2
Copyright © ickk, 2026
Licensed under the Apache License, Version 2.0 (the "License"); You may obtain
a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed
under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
CONDITIONS OF ANY KIND, either express or implied. See the License for the
specific language governing permissions and limitations under the License.
Apache License
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http://www.apache.org/licenses/
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END OF TERMS AND CONDITIONSMacros§
Structs§
- Drain
- A draining iterator for
SlimVec - Extract
If - An iterator for
SlimVecthat uses a closure to determine whether to remove an element - Into
Iter - An iterator that moves out of a
SlimVec - SlimVec
SlimVecis analogous to the Standard Library’sVeccollection type, however it has a smaller inline-size- Splice
- An iterator that moves out of a
SlimVec, replacing the removed elements with another iterator
Traits§
- Slice
Ext - Methods extending
[T]that return aSlimVec<T>