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

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 or another value, but it's the Objective-C Initialiser Idiom™.

Answer 2

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;
}

You can learn about GCC pragma here and to get the warning code of a warning go to the Log Navigator (Command+7), select the topmost build, expand the log (the '=' button on the right), and scroll to the bottom and there your warning code is within square brackets like this [-Wshadow-ivar]

---

Edit

For clang you can use

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wshadow-ivar"
// your code
#pragma clang diagnostic pop

Answer 3

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.

Answer 4

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;
}

Answer 5

_varName = varName;

You can use just this but without the @synthesize - whenever you want to use that variable you just write _*variable name* and it eliminates the error

Answer 6

If you are using local instance variable name same as global instance variable name then this warning occur.

First Methode: For ignoring this warning use have to change local instance variable name or else change the global instance variable name.

Second Methode: if you want to use global variable then call as self->variableName

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

    // super init
    self = [super init];
    if (!self) return nil;

    // set instance variables
    self->variableName = variableName; //point to global variableName
    self->comparisonValue = comparisonValue; //point to global comparisonValue

    return self;
}