weak:
/*!
Creates a __weak version of the variable provided,
which can later be safely used or converted into strong variable via @strongify.
*/
#define weakify(var) \
try {} @catch (...) {} \
__weak __typeof__(var) var ## _weak = var;
strong:
/*!
Creates a strong shadow reference of the variable provided.
Variable must have previously been passed to @weakify.
*/
#define strongify(var) \
try {} @catch (...) {} \
__strong __typeof__(var) var = var ## _weak;
