Objective-C convention to prevent “local declaration hides instance variable” warning

Question

I am using the following code ...

-(id) initWithVariableName:(NSString*)variableName withComparisonValue:(NSString*)comparisonValue {

    // super init
             


        

Answer 1

I see this is a fairly old question with a accepted answer but I have a better solution and its code convention.

The convention states that you prefix private variables with a underscore (_varName) and public (like properties) with just the name.

With this you just can call the same variable name in your functions.

Example:

ExampleClass.h

@interface ExampleClass : NSObject
{
    NSString *_varName; //this is not required if you create a property
}

@property (nonatomic, retain) NSString *varName;

- (void)someMethodWithVarName:(NSString *)varName;

@end

ExampleClass.m

#import "ExampleClass.h"

@implementation ExampleClass

@synthesize varName = _varName; //if you don't declare the _varName in the header file, Objective-C does it for you.

- (id)init
{
    self = [super init];
    if (self) {
        // Initialization code here.
    }

    return self;
}

- (void)someMethodWithVarName:(NSString *)varName
{
    _varName = varName; //just for example purpose
}

@end

Answer 2

This is not a problem at all in the modern Objective-C. In the modern Objective-C, properties are automatically synthesized and their corresponding instance variables get a _ prefix.

So, with auto-synthesis your properties would create instance variables _variableName and _comparisonValue. No shadowing occurs in this case.

More info in this blog post

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If you absolutely need to manually synthesize your properties, rename the sinthesized ivar like this

@synthesize variableName = _variableName;

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In general case, rename your method arguments.

Answer 3

You should generally prefix instance variables with something like an underscore (e.g. _variableName) to avoid compiler warnings like this.

Otherwise just slightly change the names in your method signature, there is no hard defined naming convention.