linux/errno · macos/errno · windows/errno · Standard Library

Platform-specific accessors for the C runtime error-number storage used by system and runtime wrappers. Import paths: linux/errno, macos/errno, and windows/errno.

`errno`

(-- errnoRef) Returns a borrowed mutable Int32 reference to the calling thread's C errno storage.

Each selected platform accessor is called at run time; it does not capture an error number during compilation.

Platform Code bindings

`__errno_location`

(-- errnoRef) Linux Code binding that calls the C runtime accessor and returns an Int32 Ref to the calling thread's errno storage.

`__error`

(-- errnoRef) macOS Code binding that calls the C runtime accessor and returns an Int32 Ref to the calling thread's errno storage.

`_errno`

(-- errnoRef) Windows Code binding that calls the C runtime accessor and returns an Int32 Ref to the calling thread's C errno storage, not the separate Win32 last-error state.

Read timing and overwrite

The current value is most meaningful immediately after the relevant failing call.
Later library or platform calls in the same thread may overwrite the stored value before it is read.
Snapshot an error immediately with saved: errno new; before intervening calls. This retains the previous numeric value independently of later overwrites.
saved: errno; saves a reference instead, so later writes remain visible through saved.
The accessor neither clears the stored error nor converts it into a success or failure result.

Thread-local behavior

Linux errno returns a borrowed mutable Int32 reference acquired at run time. Calls in different threads obtain their respective locations.
A saved reference stays bound to the location acquired; it is not retargeted when another thread dereferences it.
Do not free the reference or use it after its owning thread exits.

Examples

Linux runtime example

"String"      use
"control"     use
"linux/errno" use

{} Int32 {} [
  123 errno set
  errno new toString print
  LF print
  0
] "main" exportFunction