Trait polkadot_sdk_frame::arithmetic::EnsureSubAssign

pub trait EnsureSubAssign: CheckedSub + PartialOrd + Zero {
    // Provided method
    fn ensure_sub_assign(&mut self, v: Self) -> Result<(), ArithmeticError> { ... }
}

Performs self subtraction that returns ArithmeticError instead of wrapping around on underflow.

Provided Methods

fn ensure_sub_assign(&mut self, v: Self) -> Result<(), ArithmeticError>

Subtracts two numbers overwriting the left hand one, checking for overflow.

If it fails, ArithmeticError is returned.

Examples

use sp_arithmetic::traits::EnsureSubAssign;

let mut a: i32 = 10;
let b: i32 = 20;

a.ensure_sub_assign(b).unwrap();
assert_eq!(a, -10);

use sp_arithmetic::{traits::EnsureSubAssign, ArithmeticError};

fn underflow() -> Result<(), ArithmeticError> {
    let mut zero: u32 = 0;
    zero.ensure_sub_assign(1)?;
    Ok(())
}

fn overflow() -> Result<(), ArithmeticError> {
    let mut zero = i32::MAX;
    zero.ensure_sub_assign(-1)?;
    Ok(())
}

assert_eq!(underflow(), Err(ArithmeticError::Underflow));
assert_eq!(overflow(), Err(ArithmeticError::Overflow));

Object Safety

This trait is not object safe.

Implementors

impl<T> EnsureSubAssign for T

where T: CheckedSub + PartialOrd + Zero,