CODEWITHSUNDEEP
objective-c
Cai
Cai

Reputation: 451

Why declare an inital non-nil value to NSInteger before setting the intended value

This code is taken from Apples documentation on Storing Preferences in iCloud:

NSInteger reason = -1;

reason = [reasonForChange integerValue];

if ((reason == NSUbiquitousKeyValueStoreServerChange) ||
    (reason == NSUbiquitousKeyValueStoreInitialSyncChange)) {
    ...

What is the reason for declaring reason as a non-nil value?

What is wrong with directly declaring the NSInteger from the integerValue call?

NSInteger = [reasonForChange integerValue];

if ((reason == NSUbiquitousKeyValueStoreServerChange) ||
    (reason == NSUbiquitousKeyValueStoreInitialSyncChange)) {
    ...

It seems to be a different situation but if I need to declare a something outside of the scope it will be set I normally do something like this:

NSInteger reason;

if (something) {
    reason = [reasonForChange integerValue];
}

Is that incorrect? Is it something to do with it being an NSInteger? What am I missing?

Upvotes: 0

Views: 68

Answers (2)

Aruna Mudnoor
Aruna Mudnoor

Reputation: 4825

You you observe possible values for reason default value 0 is also possible value. Please check enum below

NS_ENUM(NSInteger) {
NSUbiquitousKeyValueStoreServerChange NS_ENUM_AVAILABLE(10_7, 5_0),
NSUbiquitousKeyValueStoreInitialSyncChange NS_ENUM_AVAILABLE(10_7, 5_0),
NSUbiquitousKeyValueStoreQuotaViolationChange NS_ENUM_AVAILABLE(10_7, 5_0),
NSUbiquitousKeyValueStoreAccountChange NS_ENUM_AVAILABLE(10_8, 6_0)

};

If you write something like this

NSInteger reason;

if (something) {
    reason = [reasonForChange integerValue];
}

Even if something is false the following if condition will succeed. 

if ((reason == NSUbiquitousKeyValueStoreServerChange) ||
    (reason == NSUbiquitousKeyValueStoreInitialSyncChange)) {

...

There for you have to initiate as 

NSInteger reason = -1;

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726809

What is the reason for declaring reason as a non-nil value?

There is no point in doing that. A shorter declaration/initialization that you show below, i.e.

NSInteger reason = [reasonForChange integerValue];

would work just fine, because there is no code path that leaves reason unchanged. In other words, the -1 value assigned on initialization is never read by the program, making the assignment unnecessary.

if I need to declare a something outside of the scope it will be set I normally do something like this:

NSInteger reason;

if (something) {
    reason = [reasonForChange integerValue];
}

Is that incorrect?

Yes, that would be incorrect, because when something evaluates to NO, the value of reason remains uninitialized. In this situation you should provide reason with an initial value, because reading an uninitialized local variable is undefined behavior.

Upvotes: 1

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