Example that shows the effect of scream
Introdução
Afetando o comportamento do PHP
PHP Manual

# Weak References

- Introdução
- Instalação/Configuração
  - Dependências
  - Instalação
  - Tipos de Recurso
- WeakRef — The WeakRef class
  - Weakref::acquire — Acquires a strong reference on that object
  - Weakref::__construct — Constructs a new weak reference
  - Weakref::get — Returns the object pointed to by the weak reference
  - Weakref::release — Releases a previously acquired reference
  - Weakref::valid — Checks whether the object referenced still exists
- WeakMap — The WeakMap class
  - WeakMap::__construct — Constructs a new map
  - WeakMap::count — Counts the number of live entries in the map
  - WeakMap::current — Returns the current value under iteration
  - WeakMap::key — Returns the current key under iteration.
  - WeakMap::next — Advances to the next map element
  - WeakMap::offsetExists — Checks whether a certain object is in the map
  - WeakMap::offsetGet — Returns the value pointed to by a certain object
  - WeakMap::offsetSet — Updates the map with a new key-value pair
  - WeakMap::offsetUnset — Removes an entry from the map
  - WeakMap::rewind — Rewinds the iterator to the beginning of the map
  - WeakMap::valid — Returns whether the iterator is still on a valid map element

Example that shows the effect of scream
Introdução
Afetando o comportamento do PHP
PHP Manual