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

问题:

I am using the following code ...

-(id) initWithVariableName:(NSString*)variableName withComparisonValue:(NSString*)comparisonValue {      // super init     self = [super init];     if (!self) return nil;      // set instance variables     self.mustExist = NO;     self.reverseCondition = NO;     self.regularExpression = NO;     self.variableName = variableName; // generates warning     self.comparisonValue = comparisonValue; // generates warning      return self; }

which generated the following two warnings ...

• Local declaration of 'variableName' hides instance variable
• Local declaration of 'comparisonValue' hides instance variable

Is there a common or accepted convention for dealing with these warnings?

I understand that it is simply to inform the user that they should specify an instance when referring to the class member, but its annoying.

回答1:

Unfortunately, no there's no "good" way to prevent this error. The common pattern is to use a slightly stupid parameter name like

-(id) initWithVariableName:(NSString*)theVariableName         withComparisonValue:(NSString*)theComparisonValue {     self.variableName = theVariableName;     self.comparisonValue = theComparisonValue;      return self; }

回答2:

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

回答3:

If your method truly is an initialiser, don't forget to do your self = [super init];.

- (id) initWith... {     self = [super init];     if (!self) return nil;      // do stuff      return self; }

I have never personally encountered a situation where self has changed to nil

回答4:

Either give the local a more descriptive name (e.g. initialVariableName) or give instance variables a different notation (e.g. myClass_variableName). I prefer the latter in most cases because it calls attention to when I'm using class internals rather than the proper interface.

回答5:

Though it's old question but still I've a good solution to suppress warning in code

-(id) initWithVariableName:(NSString*)variableName withComparisonValue:(NSString*)comparisonValue {      // super init     self = [super init];     if (!self) return nil;      // set instance variables     self.mustExist = NO;     self.reverseCondition = NO;     self.regularExpression = NO;       #pragma GCC diagnostic push     #pragma GCC diagnostic ignored "-Wshadow-ivar"     self.variableName = variableName; // generates warning     self.comparisonValue = comparisonValue; // generates warning     #pragma GCC diagnostic pop        return self; }

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