---
title: Signal API docs
description: All the API docs of Signal
---

# Signal API docs

Signals are the cornerstone of reactivity in `solidart`.

They contain values that change over time; when you change a signal's value, it automatically updates anything that uses it.

A __Signal__ extends a [ReadSignal](/api-docs/read-signal), so all the API of __ReadSignal__ are available.

## Constructor

```dart
Signal(
  T initialValue, {
  SignalOptions<T>? options,
});
```

`initialValue` is the initial value of the signal.

`options` are the [options](/api-docs/signal-options) of the signal.

---

```dart
Signal.lazy();
```

`Signal.lazy` is a lazy signal, it doesn't need a value at the moment of creation.
But would throw a StateError if you try to access the value before setting one.

## `set value(T newValue)`

Sets the current signal value with `newValue`.

This operation may be skipped if the value is equal to the previous one,
check [SignalOptions.equals](/api-docs/signal-options#equals) and [SignalOptions.comparator](/api-docs/signal-options#comparator).

For example:
```dart
final count = Signal(0);
count.value = 1; // set the value to 1
```

## `void set(T newValue)`

Equal to the value setter above.
This is convenient in Flutter apps where you can write:

```dart
final text = Signal('');

@override
Widget build(BuildContext context) {
  return TextField(
    onChanged: text.set,
    // instead of
    // onChanged: (value) => text.value = value,
  );
}
```

## `T updateValue(T Function(T value) callback)`

Calls a function with the __current__ value and assigns the result as the new value.

For example:
```dart
final count = Signal(2);
count.updateValue((value) => value * 2);
print(count()); // prints 4
```

## `ReadSignal<T> toReadSignal()`

Converts this __Signal__ into a __ReadSignal__.
Use this method to make the signal __read-only__.