Trait frunk_core::labelled::Transmogrifier

source · 
pub trait Transmogrifier<Target, TransmogrifyIndexIndices> {
    fn transmogrify(self) -> Target;
}
Expand description

Trait for transmogrifying a Source type into a Target type.

What is “transmogrifying”? In this context, it means to convert some data of type A into data of type B, in a typesafe, recursive way, as long as A and B are “similarly-shaped”. In other words, as long as B’s fields and their subfields are subsets of A’s fields and their respective subfields, then A can be turned into B.

Example

#[macro_use] extern crate frunk;
#[macro_use] extern crate frunk_core; // required when using custom derives
use frunk::labelled::Transmogrifier;
#[derive(LabelledGeneric)]
struct InternalPhoneNumber {
    emergency: Option<usize>,
    main: usize,
    secondary: Option<usize>,
}

#[derive(LabelledGeneric)]
struct InternalAddress<'a> {
    is_whitelisted: bool,
    name: &'a str,
    phone: InternalPhoneNumber,
}

#[derive(LabelledGeneric)]
struct InternalUser<'a> {
    name: &'a str,
    age: usize,
    address: InternalAddress<'a>,
    is_banned: bool,
}

#[derive(LabelledGeneric, PartialEq, Debug)]
struct ExternalPhoneNumber {
    main: usize,
}

#[derive(LabelledGeneric, PartialEq, Debug)]
struct ExternalAddress<'a> {
    name: &'a str,
    phone: ExternalPhoneNumber,
}

#[derive(LabelledGeneric, PartialEq, Debug)]
struct ExternalUser<'a> {
    age: usize,
    address: ExternalAddress<'a>,
    name: &'a str,
}

let internal_user = InternalUser {
    name: "John",
    age: 10,
    address: InternalAddress {
        is_whitelisted: true,
        name: "somewhere out there",
        phone: InternalPhoneNumber {
            main: 1234,
            secondary: None,
            emergency: Some(5678),
        },
    },
    is_banned: true,
};

/// Boilerplate-free conversion of a top-level InternalUser into an
/// ExternalUser, taking care of subfield conversions as well.
let external_user: ExternalUser = internal_user.transmogrify();

let expected_external_user = ExternalUser {
    name: "John",
    age: 10,
    address: ExternalAddress {
        name: "somewhere out there",
        phone: ExternalPhoneNumber {
            main: 1234,
        },
    }
};

assert_eq!(external_user, expected_external_user);
Run

Credit:

  1. Haskell “transmogrify” Github repo: https://github.com/ivan-m/transmogrify

Required Methods

Consume this current object and return an object of the Target type.

Although similar to sculpting, transmogrifying does its job recursively.

Implementors

Implementation of Transmogrifier for when the Target is empty and the Source is empty.

Implementation of Transmogrifier for identity plucked Field to Field Transforms.

Implementation of Transmogrifier for when the Target is empty and the Source is non-empty.

Non-trivial implementation of Transmogrifier where similarly-shaped Source and Target types are both Labelled HLists, but do not immediately transform into one another due to mis-matched fields, possibly recursively so.

Implementation of Transmogrifier for when the target is an HList, and the Source is a plucked HList.