Variables

Variables exposed by a C library can be declared inside a lib declaration using a global-variable-like declaration:

lib C
  $errno : Int32
  $buffer : UInt8[256]
end

Then it can be get and set:

C.errno # => some value
C.errno = 0
C.errno # => 0

C.buffer # => StaticArray(UInt8, 256)
C.buffer = StaticArray(UInt8, 256).new(0_u8)

A variable can be marked as thread local with an annotation:

lib C
  @[ThreadLocal]
  $errno : Int32
end

Refer to the type grammar for the notation used in external variables types.