Trait TryNull 

pub trait TryNull: Sized {
    type Error;

    // Required methods
    fn try_null() -> Result<Self, Self::Error>;
    fn is_null(&self) -> bool;
}

Fallible version of Null for types where null value creation can fail.

This trait is useful when:

• Null value creation requires allocation
• Validation is needed during null value construction
• Construction can fail in constrained environments
• External resources are needed to create the null value

Relationship to Null

While Null provides infallible null value creation, TryNull handles cases where construction might fail. If your type’s null value is always constructible, prefer implementing Null instead.

Thread Safety

This trait is Send + Sync safe when implemented on thread-safe types with thread-safe error types.

Examples

use multi_trait::TryNull;

#[derive(Debug)]
struct BufferId(Vec<u8>);

impl TryNull for BufferId {
    type Error = std::collections::TryReserveError;

    fn try_null() -> Result<Self, Self::Error> {
        let mut vec = Vec::new();
        vec.try_reserve(1)?;
        vec.push(0);
        Ok(BufferId(vec))
    }

    fn is_null(&self) -> bool {
        self.0.len() == 1 && self.0[0] == 0
    }
}

match BufferId::try_null() {
    Ok(null_buf) => assert!(null_buf.is_null()),
    Err(e) => eprintln!("Failed to create null buffer: {}", e),
}

Implementation Guidelines

• The error type should describe why null creation failed
• If try_null() succeeds, the result should satisfy is_null()
• The null value should be consistent across successful calls

Required Associated Types

type Error

The error type returned when null value creation fails.

Required Methods

fn try_null() -> Result<Self, Self::Error>

Try to construct a null/sentinel value of this type.

Returns Ok with a null value if successful, or Err if null value creation failed (e.g., due to allocation failure or validation error).

Errors

Returns an error if null value construction fails. The exact error conditions are type-specific.

Examples

use multi_trait::TryNull;

let null_id = ValidatedId::try_null()?;
assert!(null_id.is_null());

fn is_null(&self) -> bool

Check if this value is the null value.

Returns true if this instance represents the null/sentinel value, false otherwise. This method is identical to Null::is_null.

Examples

use multi_trait::TryNull;

let data = OptionalData::try_null().unwrap();
assert!(data.is_null());

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors