Wanted to declare and initialise a static variable in a .m file.
Objective-c compiler does not like it, and raise this error message:
Initializer element is not a compile-time constant
I like the explanation here on Stackoverflow:
Objective-C is a strict superset of C. It’s illegal in C to have any executable code outside of a function (or method in Objective-C).
Leading from this answer I discovered that I should use
dispatch_once for initialisation