Crate newstr

Simple macros for declaring String-base new types.

This crate provides simple macros that generate String based new types. The two primary macros implement the validity rules for the new type by either 1) providing a predicate that is used by the is_valid associated function, or 2) providing a function to parse and return a string which is then called by FromStr::from_str.

Both of these methods produce a new type, with the following:

1. An associated predicate function is_valid that returns true if the string provided would be a valid value for the type.
2. This type derives implementations of Clone, Debug, PartialEq, PartialOrd, Eq, Ord, and Hash.
3. An implementation of Display for T that simply returns the inner value.
4. An implementation of From<T> for String.
5. An implementation of Deref for T with the target type str.
6. An implementation of FromStr.

Example

The following example constructs a new string type that implements an Identifier value. This value must be ASCII, alphanumeric, the '_' character and must not be empty.

use std::fmt::{Display, Formatter};
use std::str::FromStr;
use std::ops::Deref;

fn is_identifier_value(s: &str) -> bool {
    !s.is_empty() && s.chars().all(|c| c.is_ascii_alphanumeric() || c == '_')
}

is_valid_newstring!(Identifier, is_identifier_value);

assert!(!Identifier::is_valid(""));
assert!(!Identifier::is_valid("hi!"));
assert!(!Identifier::is_valid("hello world"));
assert!(!Identifier::is_valid("9.99"));

assert_eq!(
    Identifier::from_str("hi").unwrap().to_string(),
    String::from("hi")
);
assert_eq!(
    Identifier::from_str("hello_world").unwrap().to_string(),
    String::from("hello_world")
);