It's not uncommon for a component to take as input a transformation function or predicate function.

For example, this PR for @angular/forms adds an @Input for a predicate function for determining if two options in a <select> are equal. Right now, this looks something like:

<select [compareWith]="equals" [(ngModel)]="selectedCountries"> ...

equals = (a: Country, b: Country) => {
   return a.id === b.id;
};

With this feature, this could be written as

<select [compareWith]="(a, b) => a.id == b.id" [(ngModel)]="selectedCountries"> ...

There are other places in Angular Material where we're looking to add similar API, e.g., datepicker with something like:

<md-datepicker [allowedDateFilter]="d => isWeekend(d)">

Or autocomplete, where the component needs to take an arbitrary value and know what string to write into the text input:

<md-autocomplete [displayWith]="value => value.getFullName()">

This would have to account for:

• Functions with multiple arguments ((a, b) => a + b)
• Functions with param names that already exist in the context (<my-x #x [uniq]="x => x.id">)
• Functions that return an object literal (x => ({name: x}))
• Invoking functions on the context (x => isActive(x)
• Passing functions through a pipe (x => x.activate() | debounce)

FYI @mhevery for planning