Objective-C @available guard AND'ed with more conditions

Question

Objective-C has an @available expression in XCode 9+ / LLVM 5+ that allows you to guard a block of code to at least a certain OS version so that it won\'t emit unguarded ava

Answer 1

Defined

#define AT_AVAILABLE(...) \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wunsupported-availability-guard\"") \
_Pragma("clang diagnostic ignored \"-Wunguarded-availability-new\"") \
__builtin_available(__VA_ARGS__) \
_Pragma("clang diagnostic pop")

Usage:

if (AT_AVAILABLE(iOS 11.0, *) && some_condition) {
    // code to run when on iOS 11+ and some_condition is true
}else {
    // code to run when on older iOS or some_condition is false
}

---

or

import this in PCH file

#pragma clang diagnostic ignored "-Wunsupported-availability-guard"
#pragma clang diagnostic ignored "-Wunguarded-availability-new"

Usage:

if (AT_AVAILABLE(iOS 11.0, *) && some_condition) {
    // code to run when on iOS 11+ and some_condition is true
}else {
    // code to run when on older iOS or some_condition is false
}

Answer 2

How about wrapping the AND up in a function?

typedef BOOL (^Predicate)();

BOOL elevenAvailableAnd(Predicate predicate)
{
    if (@available(iOS 11.0, *)) {
        return predicate();
    }
    return NO;
}

Then you only have one branch:

if (elevenAvailableAnd(^{ return someCondition })) {
    // code to run when on iOS 11+ and some_condition is true
}
else {
    // code to run when on older iOS or some_condition is false
}

Or you could do without the Block if you prefer:

BOOL elevenAvailableAnd(BOOL condition)
{
    if (@available(iOS 11.0, *)) {
        return condition;
    }
    return NO;
}

Answer 3

inline bool iOS13()
{
    if(@available(iOS 13, *))
        return true;
    else
        return false;
}

if(iOS13() && x == y)
    //...

Answer 4

You could also simply use a flag:

BOOL doit = FALSE;

if (@available(iOS 11.0, *)) {
  if (some_condition) {
    doit = TRUE;
  }
}

if (doit) {
  // code to run when on iOS 11+ and some_condition is true
} else {
  // code to run when on older iOS or some_condition is false
}

Answer 5

The way I came up with that seems to change the layout of the code the least is:

do {
  if (@available(iOS 11.0, *)) {
    if (some_condition) {
      // code to run when on iOS 11+ and some_condition is true
      break;
    }
  }
  // code to run when on older iOS or some_condition is false
} while (0);

which is still ugly.

Answer 6

You do what you always do when you have complex conditional code in the middle of a function that makes the flow complex: you hoist it into another function.

- (void)handleThing {
    if (@available(iOS 11.0, *)) {
        if (some_condition) {
            // code to run when on iOS 11+ and some_condition is true
            return;
        }
    }

  // code to run when on older iOS or some_condition is false
}

Or you hoist the check into generic code (see Josh Caswell's; it's better than how I originally wrote this).