Macro newstr::is_valid_newstring

macro_rules! is_valid_newstring {
    ($new_name:ident, $closure:expr; $( $other:ident ),*) => { ... };
    ($new_name:ident, $closure:expr) => { ... };
}

This macro takes a new type identifier and a predicate function to produce a new type. The predicate is called by T::is_valid and is then used in the implementation of FromStr to determine whether to return a new instance or error. As this is simply a boolean value and does not differentiate between reasons for invalidity the error type for FromStr is always ().

An optional variadic parameter also allows other trait names to be specified which will be added to the list of traits in the derive attribute.

Examples

Create a new string type with a user-defined closure.

is_valid_newstring!(NotEmpty, |s: &str| !s.is_empty());

assert!(!NotEmpty::is_valid(""));
assert!(NotEmpty::from_str("").is_err());

assert!(NotEmpty::is_valid("hi"));
assert!(NotEmpty::from_str("hi").is_ok());
assert_eq!(NotEmpty::from_str("hi").unwrap().len(), 2);

The following creates a new string type using an existing function.

is_valid_newstring!(AsciiStr, str::is_ascii);

In the following our new string type also derives serde attributes for serialization.

use serde::{Deserialize, Serialize};

is_valid_newstring!(NotEmpty, |s: &str| !s.is_empty(); Deserialize, Serialize);