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Roman
Roman

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Rust transpose method

#rust #option #result

Rust has a transpose method, sometimes useful, works especially well with anyhow:

use std::str::FromStr; use anyhow::Context; fn add(a: Option<&str>, b: Option<&str>) -> anyhow::Result<f32> { let a = a.map(f32::from_str).transpose()?.context("not a value")?; let b = b.map(f32::from_str).transpose()?.context("not a value")?; Ok(a + b) } fn main() { println!("{:?}", add(Some("12"), Some("1.2"))); println!("{:?}", add(Some("a"), Some("1.2"))); println!("{:?}", add(None, Some("1.2"))); }
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output:

Ok(13.2) Err(invalid float literal) Err(not a value)
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