Struct Validator 

pub struct Validator(/* private fields */);

A boxed, state-capturing field validator.

Unlike the deprecated FormValidator function pointer, a Validator wraps a closure, so it can capture surrounding state — a compiled matcher, a min/max pulled from config, or a sibling field’s value. Built-in constructors live in the validators module.

You rarely construct one directly: FormField::validate accepts a closure and boxes it for you. Use Validator::new when you need to build a Validator value yourself.

Example

let min = 3usize; // captured state — impossible with a fn pointer
let v = Validator::new(move |s: &str| {
    if s.len() >= min { Ok(()) } else { Err(format!("min {min} chars")) }
});
assert!(v.run("hello").is_ok());
assert!(v.run("hi").is_err());

Implementations

impl Validator

pub fn new(f: impl Fn(&str) -> Result<(), String> + 'static) -> Self

Wrap a closure as a Validator.

The closure may capture state (it is Box<dyn Fn>, not a function pointer).

pub fn run(&self, value: &str) -> Result<(), String>

Run the validator against value, returning its Err message on failure.

Trait Implementations

impl Debug for Validator

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.