Crate boulder

Expand description

This crate is based around two traits, Buildable and Generatable, and their associated derive macros, which provide ways to construct objects succinctly.

Builder

A Builder is a way to create a single object, specifying only the fields you wish to give non-default values. The default values are specified using attributes on your type for ease of reading. Each field gains a method of the same type in the builder which can be be used to customise it.

Example

use boulder::{Builder, Buildable};
#[derive(Buildable)]
struct Foo {
   #[boulder(default=5)]
   pub a: i32,
   #[boulder(default="hello")]
   pub b: String,
}

let f = Foo::builder()
         .a(27)
         .build();
assert_eq!(f.a, 27);
assert_eq!(f.b, "hello".to_string());

Generator

A Generator is a way to create an infinite sequence of objects, again specifying only the functions for generating the fields you wish to have non-default sequences. The default sequences are specified using attributes on your type for ease of reading. Each field gains a method of the same name in the generator, which can be be used to customise the sequence of values produced for that field as objects are made.

Example

use boulder::{Generator, Generatable, Inc, Pattern};
#[derive(Generatable)]
struct Bar {
   #[boulder(generator=Inc(1i32))]
   pub a: i32,
   #[boulder(generator=Pattern!("hello-{}-foo", Inc(5i32)))]
   pub b: String,
}

let mut n = 2;
let mut gen = Bar::generator()
     .a(move || {
         n = n + 2;
         n
});

let bar1 = gen.generate();
assert_eq!(bar1.a, 4);
assert_eq!(bar1.b, "hello-5-foo".to_string());

let bar2 = gen.generate();
assert_eq!(bar2.a, 6);
assert_eq!(bar2.b, "hello-6-foo".to_string());

persian-rug

When the "persian-rug" feature is enabled, a parallel set of types, traits and derive macros are enabled, i.e. BuildableWithPersianRug and GeneratableWithPersianRug. These provide similar facilities, but for types based on the persian-rug crate.

Briefly, persian-rug moves ownership of all values into a single container (the “rug” or Context). Client code then deals with handles (in the form Proxy<T>) to these values. The builders and generators take a mutator for the type’s context in their build and generate methods, which means at the point of construction, the set of other constructed instances (of all types in that context) is available.

Since the derived generators pass through Proxy<T>, and since to get the most benefit from this system you should work with proxies where possible, the most common usage is to use these solely through the pass throughs.

Example:

use boulder::{BuilderWithPersianRug, BuildableWithPersianRug};
use persian_rug::{contextual, persian_rug, Context, Proxy};

#[persian_rug]
struct Rug(
  #[table] Foo,
  #[table] Bar,
);

#[contextual(Rug)]
#[derive(BuildableWithPersianRug)]
#[boulder(persian_rug(context=Rug))]
struct Foo {
   #[boulder(default=5)]
   pub a: i32,
   #[boulder(buildable_with_persian_rug(a=5))]
   pub b: Proxy<Bar>,
}

#[contextual(Rug)]
#[derive(BuildableWithPersianRug)]
#[boulder(persian_rug(context=Rug))]
struct Bar {
  #[boulder(default=2)]
  pub a: i32
}

let mut r = Rug(Default::default(), Default::default());
let (f, _) = Proxy::<Foo>::builder()
         .a(27)
         .build(&mut r);
assert_eq!(r.get(&f).a, 27);
assert_eq!(r.get(&r.get(&f).b).a, 5);