Derive Macro robma_builder::Builder

#[derive(Builder)]
{
    // Attributes available to this derive:
    #[builder]
}

Derives a builder() method that can be used to construct an instance of a struct.

The library is implemented using a procedural macro. The builder is a fluent-design pattern that simplifies the construction of a struct instance. In particular, we support the following features

• No uninitialized members: checks the presence of all variables and panics in case of missing variables.
• Members of type Option do not have to be specified and default to None
• Repeated arguments: Members of type Vec can be constructed using a sequence of individual elements.

Examples:

Basic usage

use robma_builder::Builder;

#[derive(Builder, Debug, PartialEq)]
pub struct Command {
    executable: String,
    args: Vec<String>,
    env: Vec<String>,
    current_dir: String,
}

let command = Command::builder()
       .executable("cargo".into())
       .args(vec!["build".into(), "--release".into()])
       .env(vec![])
       .current_dir("..".into())
       .build()
       .expect("missing arguments");

// The result of the above is equivalent to:
let command_equivalent = Command{
        executable: "cargo".into(),
        args: vec!["build".into(), "--release".into()],
        env: vec![],
        current_dir: "..".into(),
};
assert_eq!(command, command_equivalent);

Optional members

Optional members can be ommitted in the builder and initialized with None

use robma_builder::Builder;

#[derive(Builder)]
pub struct Command {
    current_dir: Option<String>,
}

let command = Command::builder()
    .build()
    .expect("missing arguments");

// Unspecified option members will be initialized with None:
assert!(command.current_dir.is_none());

Repeated arguments

Members of type Vec can be initialized by a sequence of elements. Use the attribute #[builder(each = "...")] to declare the name of the function.

use robma_builder::Builder;

#[derive(Builder)]
pub struct Command {
    #[builder(each = "arg")]
    args: Vec<String>,
}

let command = Command::builder()
    .arg("build".to_owned())
    .arg("--release".to_owned())
    .build()
    .expect("missing arguments");

// args contains the elements of each call to `arg()`
assert_eq!(command.args, vec!["build", "--release"]);