bug or docs issue: filters are always invoked for object inputs (regardless of identity or value equality)

[bughit]

https://plnkr.co/edit/d0J4zqlTZvrsSJvywM0y?p=preview

for primitive inputs, the filter is invoked only if the value changes

docs:

The filter function should be a pure function, which means that it should be stateless and idempotent. Angular relies on these properties and executes the filter only when the inputs to the function change.

so is the behavior for objects a feature or a bug?

[Narretz]

This is expected behavior, as it's too expensive to keep a copy of an object around to determine if the object changed, see

angular.js/src/ng/parse.js

Lines 1991 to 2004 in eebbca0

	if (typeof newValue === 'object') {
	// attempt to convert the value to a primitive type
	// TODO(docs): add a note to docs that by implementing valueOf even objects and arrays can
	// be cheaply dirty-checked
	newValue = getValueOf(newValue);
	if (typeof newValue === 'object') {
	// objects/arrays are not supported - deep-watching them would be too expensive
	return false;
	}
	// fall-through to the primitive equality check
	}

Do you want to submit a PR that updates the docs about this?