Built In Types: Resources

A resource is a descriptor to some sort of external entity. (Examples include files, databases, and sockets.) Resources are only created or consumed by the implementation; they are never created or consumed by Hack code. Each distinct resource has a unique ID of some unspecified form.

When scripts execute in a mode having a command-line interface, the following resources that correspond to file streams are automatically opened at program start-up:

• HH\\stdin() or HH\\try_stdin(), which map to standard input
• HH\\stdout() or HH\\try_stdout(), which map to standard output
• HH\\stderr() or HH\\try_stderr(), which map to standard error

These streams have some unspecified type, which behaves like a subtype of type resource.

The try variants return null when executed without a command-line interface, while the non-try functions throw an exception.

Resources are a carryover from PHP, and their use is discouraged in Hack code.