Engineer

Engineer is a master builder based on Optional.

It just generates an Engineer (Builder) class for a data model.

Installation

Add following as dependencies

[dependencies]
engineer = "0.1.3"

Get Started

use engineer::Engineer;

#[derive(Engineer)]
struct Identity {
    id: usize,
    username: String,
    first_name: Option<String>,
    last_name: Option<String>,
    lang_code: Option<String>,
}

Optional fields are not required during the initialization.

// Option fields are set to None.
let identity = Identity::engineer(0, "immmdreza".to_string()).done();

But you can set a value for Option fields as well.

let identity = Identity::engineer(0, "immmdreza".to_string()) // IdentityEngineer
    .first_name("Arash".to_string()) // IdentityEngineer
    .last_name("Tofani".to_string()) // IdentityEngineer
    .done(); // Identity

That's all for the basics, but you can do a little customizations.

Customizations

Engineer Struct Name

Engineer struct name is {struct}Engineer (IdentityEngineer for Identity) by default, but you can change that.

// ~~~ sniff ~~~

#[derive(Engineer)]
#[engineer(engineer_name = "IdentityBuilder")]
struct Identity {
    // ~~~ sniff ~~~
}

// ~~~ sniff ~~~

    let identity = Identity::engineer(0, "immmdreza".to_string()) // IdentityBuilder
        .first_name("Arash".to_string()) // IdentityBuilder
        .last_name("Tofani".to_string()) // IdentityBuilder
        .done(); // Identity

Builder Function Name

The name of builder function is engineer by default, but guess what?

// ~~~ sniff ~~~

#[derive(Engineer)]
#[engineer(builder_func = "builder")]
struct Identity {
    // ~~~ sniff ~~~
}

// ~~~ sniff ~~~

    let identity = Identity::builder(0, "immmdreza".to_string())
    // ~~~ sniff ~~~

You want to use this as new function:

// ~~~ sniff ~~~

#[derive(Engineer)]
#[engineer(builder_func = "new")]
struct Identity {
    // ~~~ sniff ~~~
}

// ~~~ sniff ~~~

    let identity = Identity::new(0, "immmdreza".to_string())
    // ~~~ sniff ~~~

This can be simplified for special new name as builder function:

#[derive(Engineer)]
#[engineer(new)]
struct Identity {
    // ~~~ sniff ~~~
}

Default value for Options

You can set a default value for option fields.

This value is used if you don't set any other for them.

// ~~~ sniff ~~~

#[derive(Engineer)]
#[engineer(new)]
struct Identity {
    // ~~~ sniff ~~~
    #[engineer(default_value = r#"String::from("fa")"#)]
    lang_code: Option<String>,
}

// ~~~ sniff ~~~

    let identity = Identity::new(0, "immmdreza".to_string());

    identity.lang_code // Some("fa")

Alternatively, you can use default to set Some(Default::default) instead of None if any other value is not given.

    // ~~~ sniff ~~~
    #[engineer(default)]
    luck_number: Option<i32>, // Some(0)
    // ~~~ sniff ~~~

Retype

You can change types requested in builder processes.

// ~~~ sniff ~~~

#[derive(Engineer)]
#[engineer(new)]
struct Identity {
    // ~~~ sniff ~~~
    #[engineer(retype(to = "impl Into<String>", re = ".into()"))]
    //                      ^                         ^
    //                      | Requested type in public.
    //                                                |
    //                                                | How we recover to original type.
    username: String,
    // ~~~ sniff ~~~
}

// ~~~ sniff ~~~

    let identity = Identity::new(0, "immmdreza"); // .to_string() is not needed.
    // ~~~ sniff ~~~

Alternatively, for str retypes (like example above), you can use a shorthand str_retype.

    // ~~~ sniff ~~~
    #[engineer(str_retype)]
    username: String,
    // ~~~ sniff ~~~

Also you can use retypes globally.

#[derive(Engineer)]
#[engineer(new, retype(from = "String", to = "impl Into<String>", re = ".into()"))]
struct Identity {
    // ~~~ sniff ~~~
}

Or additionally for String retypes:

#[derive(Engineer)]
#[engineer(new, str_retype)]
struct Identity {
    // ~~~ sniff ~~~
}

Both codes above will retype all String fields into impl Into<String> in public api.

Final result

#[derive(Engineer)]
#[engineer(new, str_retype)]
struct Identity {
    id: usize,
    username: String,
    first_name: String,
    last_name: Option<String>,
    #[engineer(str_retype, default_value = "\"fa\".to_string()")]
    lang_code: Option<String>,
}

fn print_identity(ident: impl Into<Identity>) {
    let ident: Identity = ident.into();
    println!("{ident:#?}");
}

fn main() {
    let ident = Identity::new(1, "immmdreza", "Arash").last_name("Tofani");

    print_identity(ident);
    // Identity {
    //     id: 1,
    //     username: "immmdreza",
    //     first_name: "Arash",
    //     last_name: Some(
    //         "Tofani",
    //     ),
    //     lang_code: Some(
    //         "fa",
    //     ),
    // }
}

More about traits

This crate has two main traits: Builder<T> where T: Engineer and Engineer.

Engineer trait has two associated types: Params and Builder.

• Params is a tuple of your required fields types ( fields that are not Option<_> )
• Builder is the type of Builder/Engineer class.

Using Engineer macro, will make your data class implements Engineer trait and also creates a Builder struct ( usually named {struct_name}Engineer - i'm thinking about rename ) that implements Builder<T> where T is your own struct.

This enables you to do some generic stuff around these traits, As instance:

fn build_any<E>(required: E::Params) -> E
where
    E: Engineer,
{
    E::build(required)
}

// Or

fn get_builder<E>(required: E::Params) -> E::Builder
where
    E: Engineer,
{
    E::builder(required)
}

Note that E::Params is a tuple.

If all of you required fields (E::Param) implement Default, another function build_default will become available on you struct that creates a default instance with no inputs required.

Additionally, Engineer trait has two const fields:

- const NORMAL_FIELDS: usize;
- const OPTIONAL_FIELDS: usize;

🧀