Question

I’m more of an Android developer, but i’m beginning to see the light at the end of the tunnel on iOS development.

There is, however, one coding pattern I can’t seem to find an equivalent for.

The use of static fields as flags.

Android :

public final static int ERROR_EMPTY = 1;
public final static int ERROR_NO_CONNECTION = 2;
public final static int ERROR_WRONG_USER = 4;

...

if (error == MyClass.ERROR_EMPTY) {//do things}

What would be the proper way to achieve this on iOS ?

Thanks.

Answer 1

Using Objective-C and C

i often use prefixes:

typedef enum MyClass_Error {
  // never use MyClass_Error_Undefined
  // or you may favor MyClass_Error_None for a valid error code
  MyClass_Error_Undefined = 0,
  MyClass_Error_Empty = 1,
  MyClass_Error_NoConnection = 2,
  MyClass_Error_WrongUser = 4
  // ...
} MyClass_Error;

for these value collections. then you get benefits such as typesafety and switch value checking.

for non-type constants:

enum { MyClass_ConstantName = 4 };

and feel free to hide these in the *.m when private.

also note that C enums may have gaps in their defined values (unlike Java’s).

Update: there’s an even better way to declare an enum, as demonstrated in Abizern’s answer — if you’re sticking with the most recent toolchains. the big reason to use this extension is for binary compatibility and encoding (although i favor fixed-width types for these purposes).

---

There are a few other variations, for the cases when you want to use existing types:

Private Constant

MyClass.m

static const NSRange MyClass_InputRange = {1,1};

Public Constant

MyClass.h

extern const NSRange MyClass_InputRange;

MyClass.m

const NSRange MyClass_InputRange = {1,1};

---

Using C++

You would likely favor introducing a new scope for these values — either in a class or a namespace, rather than simulating the scope using prefixes.

Common Mistakes

• Use of #define for constants (unless definition is mandatory when preprocessing)
• Use of short identifiers, and identifiers which are not prefixed
• Use of static values in headers
• Not using const when possible
• Declaring them in the header, when they could be in the *.m source.