exit status: 1 with stderr:
<stdin>:8:17: error: reference to property 'a' in closure requires explicit use of 'self' to make capture semantics explicit a += 1 ^ <stdin>:7:20: note: variable other than 'self' captured here under the name 'self' does not enable implicit 'self' foo { [self] in ^ <stdin>:7:20: warning: capture 'self' was never used foo { [self] in ^