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 AsRef for T with the target type str.
6. An implementation of Deref for T with the target type str.
7. An implementation of FromStr.

Additional user-required traits can also be added to the macro to be derived by the implementation.

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;

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")
);

The macro new_unchecked will add a constructor to the type that allows a trusted client to bypass the validity checks.

new_unchecked!(pub(crate) Identifier);

assert_eq!(
    Identifier::from_str("hi").unwrap(),
    Identifier::new_unchecked("hi")
);

Dependencies

In the example above you can see the necessary use-statements for the trait implementations the macros generate. Unless you use regex_is_valid there are no crate dependencies; if you do you will need to add lazy_static and regex dependencies.

Changes

Version 0.2.0

• Changes to the macro API;
  • use ; instead of , to separate the additional derive macros,
  • use full paths inside all macros, no need for the use_required macro any more,
  • clients will need to import any trait they then use such as FromStr.
• Added new_unchecked macro for validity bypass.

Version 0.1.2

• Added additional, optional, parameter to both macros that allows additional traits to be added to the derive attribute on the generated struct.
• Refactored the macros to reduce repetition.
• Added some additional tests.

Version 0.1.1

• Added new use_required macro.
• Removed unnecessary feature 'regex_is_valid', the build doesn't require this to avoid bloat.
• Made lazy_static and regex dev dependencies, if you don't use them, you don't need them.
• Added dependency on cargo-husky for Git cleanliness.

Version 0.1.0

• Initial version.