Consider a typed group for storing contact information:
```
declare interface ContactControls {
name: FormControl<string|null>;
}
contactForm: FormGroup<ContactControls> = ...;
saveForm(form: FormGroup<ContactControls>) {
service.newContact(contactForm.value);
}
```
What should be the type of `newContact`? The answer, of course, is the value type:
```
declare interface Contact {
name: string|null;
}
class ContactService {
newContact(c: Contact) {}
}
```
This is quite redundant, and therefore, we should allow the value type to be generated automatically. We already have the helper types to do this -- we just need to document and export them. Then, this becomes possible:
```
class ContactService {
newContact(c: RawValue<FormGroup<ContactControls>>) {}
}
```
PR Close#45978
This PR strongly types the forms package by adding generics to AbstractControl classes as well as FormBuilder. This makes forms type-safe and null-safe, for both controls and values.
The design uses a "control-types" approach. In other words, the type parameter on FormGroup is an object containing controls, and the type parameter on FormArray is an array of controls.
Special thanks to Alex Rickabaugh and Andrew Kushnir for co-design & implementation, to Sonu Kapoor and Netanel Basal for illustrative prior art, and to Cédric Exbrayat for extensive testing and validation.
BREAKING CHANGE: Forms classes accept a generic.
Forms model classes now accept a generic type parameter. Untyped versions of these classes are available to opt-out of the new, stricter behavior.
PR Close#43834
model.ts is currently extremely large. This is the first step in an attempt to refactor it to be more easily navigable and reviewable. This commit breaks up `model.ts` into the following new files:
* `model/abstract_model.ts`: The remainder of the model, including the `AbstractControl` base class and helper functions which are used throughout.
* `model/form_control.ts`: `FormControl`, `FormControlOptions`, and helpers, plus the constructor and untyped friends.
* `model/form_array.ts`: `FormArray` and untyped friends.
* `model/form_group.ts`: `FormGroup` and untyped friends.
This first phase is a purely mechanical code move. There is no new code at all, and no interfaces have been separated.
PR Close#45217
