inline-option

Provides the Nullable trait for describing nullable values, and IOption, an optional type that wraps a Nullable value inline without extra space overhead.

In certain performance-intensive applications, the standard library's Option enum type can be wasteful because Rust enums are tagged unions with a discriminant. The discriminant takes up extra space in memory, which can be undesirable when working with small, primitive types. For instance, Option<f32> has a size of 8 bytes on 64-bit systems, while f32 has a size of only 4 bytes. This can be unoptimal when working with large arrays of optional values, in terms of both memory usage and cache efficiency.

IOption is a thin wrapper around a nullable value that provides a similar API to Option, but without the extra space overhead. It is a zero-cost abstraction that is as efficient as working with the nullable value directly.

Example

use inline_option::{IOption, Nullable};

// Define a struct that can be null.
#[derive(Clone, Copy, Debug, PartialEq)]
struct Value(i32);

// Implement the Nullable trait for the struct.
impl Nullable for Value {
    const NULL: Self = Value(i32::MAX);

    fn is_null(&self) -> bool {
        self.0 == i32::MAX
    }
}

fn main() {
    // Create an inline option that can hold a Value.
    let mut opt = IOption::<Value>::none();
    assert!(opt.is_none());

    // Replace the value in the inline option.
    opt.replace(Value(42));
    assert!(opt.is_some());

    // Get the value from the inline option.
    let value = opt.unwrap();
    assert_eq!(value.0, 42);

    // Or, convert it to a standard option.
    let std_opt = opt.as_ref();
    assert_eq!(std_opt, Some(&Value(42)));
}

Benchmarks

Based on the simple benchmark in benches/bench.rs, Vec<IOption<T>> can be iterated over 3 times as fast as Vec<Option<T>>:

Cargo Features

• serde: Enables Serde 1 support for IOption.
• nullable-core-floats: Implements Nullable for f32 and f64, using their maximum values as their null values.
• nullable-core-ints: Implements Nullable for i8 through i128, u8 through u128, isize, and usize using their maximum values as their null values.

License

MIT OR Apache-2.0