cascade: Cascade expressions in Rust!

cascade is a macro library for Rust that makes it easy and ergonomic to use cascade-like expressions, similar to Dart.

#[macro_use]
extern crate cascade;

fn main() {
    let cascaded_list = cascade! {
      Vec::new();
      ..push("Cascades");
      ..push("reduce");
      ..push("boilerplate");
    };
    println!("{:?}", cascaded_list); // Will print '["Cascades", "reduce", "boilerplate"]'
}

This is only a small example of what cascade lets you do: the basic_cascades example in this repository covers the other cool features of the cascade! macro.

Why does this need to exist?

Cascades reduce boilerplate by eliminating the need for a 'temporary' variable when making several method calls in a row, and it also helps make struct member assignments look more ergonomic. For example:

#[macro_use]
extern crate cascade;

#[derive(Clone, Debug)]
struct Person {
  pub name: String,
  pub age: u32,
  pub height: u32,
  pub friend_names: Vec<String>
}

fn main() {
    // Without cascades
    let person = Person {
      name: "John Smith",
      age: 17,
      height: 68, // 5' 8"
      friend_names: {
        let mut tmp_names = Vec::new();
        tmp_names.push("James Smith".to_string());
        tmp_names.push("Bob Jones".to_string());
        tmp_names.push("Billy Jones".to_string());
        tmp_names
      }
    };
    // With cascades
    let person = Person {
      name: "John Smith",
      age: 17,
      height: 68,
      friend_names: cascade! {
        Vec::new();
        ..push("James Smith".to_string());
        ..push("Bob Jones".to_string());
        ..push("Billy Jones".to_string());
      }
    };
    // Cascades also let you do cool stuff like this
    let person_one_year_later = cascade! {
      person;
      ..age += 1;
      ..height += 2;
    };
}

In addition, cascades make it easier to design fluent interfaces. No more returning self with every single function!

Changelog

1.0.0: cascade has reached 1.0! Here are some of the cool new features and syntax changes made as a part of this:

• The syntax for binding variables has been changed to use let syntax. This makes it more in-line with Rust syntax and also allows you to specify the type of a cascaded expression.

cascade! {
    // If you don't need to bind the statement to an identifier, you can use _
    let _: Vec<u32> = vec![1,2,3].into_iter().map(|x| x + 1).collect();
    ..push(1);
}

• Statements no longer need | in front of them. You can just put the statement right in there, no prefix needed.
• You can return expressions from cascades, just like normal Rust blocks. By default, cascades will already return the value of the cascaded variable. But if you want to return a custom expression, you can put it at the end of a cascade block, with no semicolon.

let has_more_than_three_elements = cascade! {
    let v = vec![1,2,3];
    ..push(4);
    v.len() > 3
};
println!("{}", cascade! {
    vec![1,2,3];
    ..push(4);
    ..into_iter().fold(0, |acc, x| acc + x)
});

• Finally, you can have nested blocks within a cascade block. For example:

cascade! {
    vec![1,2,3];
    {
        let a = 1;
        ..push(a);
    };
}

I hope you enjoy cascade 1.0! Remember to leave any complaints or suggestions on the issue tracker.

0.1.3: The ? operator now works with cascades, for scenarios like this:

fn file_read() -> Result<SomeFileClass, ErrorMsg> {
    cascade! {
      SomeFileClass::create_file_reader("test.txt");
      ..load()?;
      ..check_validity()?;
    }
}

0.1.2: You can now chain methods together, like this:

fn chain_example() {
  cascade! {
    FnChainTest::new();
    ..chain().chain().chain();
  }
}

Credits

Written by Jane Lewis