Derived Signals with map()

Signals can be transformed into derived values for binding. This is useful when the source state is not the exact shape you want to display.

Creating a derived value with map()

For example, if we have a signal containing a full name, we can derive the first character for display:

use vizia::prelude::*;

pub struct AppData {
    pub name: Signal<String>,
}

impl Model for AppData {}

fn main() -> Result<(), ApplicationError> {
    Application::new(|cx| {
        let name = Signal::new(String::from("John Doe"));

        AppData { name }.build(cx);

        Label::new(cx, name.map(|name| name.chars().next().unwrap_or('?')));
    })
    .inner_size((400, 100))
    .run()
}

When name changes, the label updates automatically because the derived signal is still reactive.

Derived signals are also useful for:

• Converting numbers to formatted strings.
• Mapping enums to UI labels or colors.
• Computing booleans for disabled, checked, or class toggles.

map() vs Memo::new

• Use signal.map(...) for simple one-signal transforms.
• Use Memo::new(...) when combining multiple signals, reusing the derived value, or when an explicit named derived value improves readability.

Internally, map() also produces a memoized derived value.

See also

• Memos
• Reading Signals