Advanced component props

Documenting parameters

Documentation is important to ensure components are easy to use and understand. Parameters can be documented with standard Rust documentation comments and attributes:

#![allow(unused)]
fn main() {
use avalanche::{component, tracked, View};
use avalanche_web::components::Text;

/// Repeats a character for the specified number of times.
#[component]
fn Repeat(
    /// The character to repeat.
    character: char, 
    #[doc = "How many times the character is repeated."]
    n: usize,
) -> View {
    Text(self, tracked!(character).to_string().repeat(tracked!(n)))
}
}

Default parameters

Imagine that we wanted to hide the Repeat component if the user does not supply a value for n. We can do this by using usize's default value:

#![allow(unused)]
fn main() {
use avalanche::{component, tracked, View};
use avalanche_web::components::Text;

#[component]
fn Repeat(
    character: char, 
    // How many times the character is repeated.
    #[default]
    n: usize
) -> View {
    Text(self, tracked!(character).to_string().repeat(tracked!(n)))
}
}

Specifying custom default values is also possible. If we want to make Repeat excitement-themed, we could choose a default character value '!':

#![allow(unused)]
fn main() {
use avalanche::{component, tracked, View};
use avalanche_web::components::Text;

#[component]
fn Repeat(
    #[default = '!']
    character: char, 
    #[default]
    // How many times the character is repeated.
    n: usize
) -> View {
    Text(self, tracked!(character).to_string().repeat(tracked!(n)))
}
}

The component can now be called with Repeat(self), which would render nothing, or Repeat(self, count = 3), which would render !!!.

A default value can be any valid Rust expression. The expression will only be evaluated if the caller of the component does not supply their own value.

Generic components

Generic components can be written similarly to generic functions:

#![allow(unused)]
fn main() {
use avalanche::{component, tracked, View};
use avalanche_web::components::Text;
use std::string::ToString;

#[component]
fn SayHello<S: ToString>(name: S) -> View {
    Text(self, format!("Hello, {}!", tracked!(name).to_string()))
}
}

Note that impl Trait properties are not supported in components.