What's going on in NSCFBoolean and NSNumber?
Ok, so I have an NSDictionary that holds a boolean value. It's loaded from the server and parsed by the framework, and for some reason it ends up being stored as an NSCFBoolean in the dictionary (don't ask, all I know is that the -class method returns __NSCFBoolean).
Since NSCFBoolean is a framework-private class that I cannot use directly, I make a reference to it:
id myBool = myDict[@"my_bool"];
Now comes the cool part: evaluating it. I used a breakpoint and the "po" command. These are the results:
> po myBool
0
> po [myBool class]
__NSCFBoolean
> po [myBool boolValue]
<nil>
What the..?
> po myBool == true
false
> po myBool == false
<nil>
brain melts
How is it possible that == true returns false and == false returns nil?
I have a number of years of experience in programming in Objective-C but I have never seen this weird behaviour before! I've read several articles about the differences between the different boolean types and their behaviours and quirks (This article at NSHipster is quite interesting) but I've read nothing that would explain this behaviour.
objective-c boolean
asked Nov 23 '18 at 10:53
MarkMark
378314
add a comment |
Ok, so I have an NSDictionary that holds a boolean value. It's loaded from the server and parsed by the framework, and for some reason it ends up being stored as an NSCFBoolean in the dictionary (don't ask, all I know is that the -class method returns __NSCFBoolean).
Since NSCFBoolean is a framework-private class that I cannot use directly, I make a reference to it:
id myBool = myDict[@"my_bool"];
Now comes the cool part: evaluating it. I used a breakpoint and the "po" command. These are the results:
> po myBool
0
> po [myBool class]
__NSCFBoolean
> po [myBool boolValue]
<nil>
What the..?
> po myBool == true
false
> po myBool == false
<nil>
brain melts
How is it possible that == true returns false and == false returns nil?
I have a number of years of experience in programming in Objective-C but I have never seen this weird behaviour before! I've read several articles about the differences between the different boolean types and their behaviours and quirks (This article at NSHipster is quite interesting) but I've read nothing that would explain this behaviour.
objective-c boolean
asked Nov 23 '18 at 10:53
MarkMark
378314
2
Most of the confusion is caused by the fact that the compiler treatsmyBoolasid(void pointer) although[myBool class]prints__NSCFBoolean. For example this explains[myBool boolValue]==nilbecauseidhas no methodboolValue.
– vadian
Nov 23 '18 at 11:20
2
And> p [myBool boolValue]returns what? Be careful withpo, since it's object, if it' 0, often it prints nil instead of false or 0 as you expect, usepwhen it's the case for check.
– Larme
Nov 23 '18 at 13:49
__NSCFBooleanis returned from@NO,@YES,[NSNumber numberWithBool:NO]and[NSNumber numberWithBool:YES].
– Willeke
Nov 24 '18 at 1:42
@Vadian id is not the same as void pointer, see What is the meaning of id?.[myBool boolValue]will send selectorboolValuetomyBool, howmyBoolis declared doesn't matter. The superclass of__NSCFBooleanisNSNumberand[myBool boolValue]==nilbecause[myBool boolValue]returnsNOwhichpo(print object) will print as<nil>.
– Willeke
Nov 24 '18 at 2:00
add a comment |
Ok, so I have an NSDictionary that holds a boolean value. It's loaded from the server and parsed by the framework, and for some reason it ends up being stored as an NSCFBoolean in the dictionary (don't ask, all I know is that the -class method returns __NSCFBoolean).
Since NSCFBoolean is a framework-private class that I cannot use directly, I make a reference to it:
id myBool = myDict[@"my_bool"];
Now comes the cool part: evaluating it. I used a breakpoint and the "po" command. These are the results:
> po myBool
0
> po [myBool class]
__NSCFBoolean
> po [myBool boolValue]
<nil>
What the..?
> po myBool == true
false
> po myBool == false
<nil>
brain melts
How is it possible that == true returns false and == false returns nil?
I have a number of years of experience in programming in Objective-C but I have never seen this weird behaviour before! I've read several articles about the differences between the different boolean types and their behaviours and quirks (This article at NSHipster is quite interesting) but I've read nothing that would explain this behaviour.
objective-c boolean
asked Nov 23 '18 at 10:53
MarkMark
378314
Ok, so I have an NSDictionary that holds a boolean value. It's loaded from the server and parsed by the framework, and for some reason it ends up being stored as an NSCFBoolean in the dictionary (don't ask, all I know is that the -class method returns __NSCFBoolean).
Since NSCFBoolean is a framework-private class that I cannot use directly, I make a reference to it:
id myBool = myDict[@"my_bool"];
Now comes the cool part: evaluating it. I used a breakpoint and the "po" command. These are the results:
> po myBool
0
> po [myBool class]
__NSCFBoolean
> po [myBool boolValue]
<nil>
What the..?
> po myBool == true
false
> po myBool == false
<nil>
brain melts
How is it possible that == true returns false and == false returns nil?
I have a number of years of experience in programming in Objective-C but I have never seen this weird behaviour before! I've read several articles about the differences between the different boolean types and their behaviours and quirks (This article at NSHipster is quite interesting) but I've read nothing that would explain this behaviour.
objective-c boolean
objective-c boolean
asked Nov 23 '18 at 10:53
MarkMark
378314
asked Nov 23 '18 at 10:53
MarkMark
378314
asked Nov 23 '18 at 10:53
MarkMark
378314
asked Nov 23 '18 at 10:53
MarkMark
378314
asked Nov 23 '18 at 10:53
MarkMark
378314
378314
2
Most of the confusion is caused by the fact that the compiler treatsmyBoolasid(void pointer) although[myBool class]prints__NSCFBoolean. For example this explains[myBool boolValue]==nilbecauseidhas no methodboolValue.
– vadian
Nov 23 '18 at 11:20
2
And> p [myBool boolValue]returns what? Be careful withpo, since it's object, if it' 0, often it prints nil instead of false or 0 as you expect, usepwhen it's the case for check.
– Larme
Nov 23 '18 at 13:49
__NSCFBooleanis returned from@NO,@YES,[NSNumber numberWithBool:NO]and[NSNumber numberWithBool:YES].
– Willeke
Nov 24 '18 at 1:42
@Vadian id is not the same as void pointer, see What is the meaning of id?.[myBool boolValue]will send selectorboolValuetomyBool, howmyBoolis declared doesn't matter. The superclass of__NSCFBooleanisNSNumberand[myBool boolValue]==nilbecause[myBool boolValue]returnsNOwhichpo(print object) will print as<nil>.
– Willeke
Nov 24 '18 at 2:00
add a comment |
2
Most of the confusion is caused by the fact that the compiler treatsmyBoolasid(void pointer) although[myBool class]prints__NSCFBoolean. For example this explains[myBool boolValue]==nilbecauseidhas no methodboolValue.
– vadian
Nov 23 '18 at 11:20
2
And> p [myBool boolValue]returns what? Be careful withpo, since it's object, if it' 0, often it prints nil instead of false or 0 as you expect, usepwhen it's the case for check.
– Larme
Nov 23 '18 at 13:49
__NSCFBooleanis returned from@NO,@YES,[NSNumber numberWithBool:NO]and[NSNumber numberWithBool:YES].
– Willeke
Nov 24 '18 at 1:42
@Vadian id is not the same as void pointer, see What is the meaning of id?.[myBool boolValue]will send selectorboolValuetomyBool, howmyBoolis declared doesn't matter. The superclass of__NSCFBooleanisNSNumberand[myBool boolValue]==nilbecause[myBool boolValue]returnsNOwhichpo(print object) will print as<nil>.
– Willeke
Nov 24 '18 at 2:00
2
2
Most of the confusion is caused by the fact that the compiler treats
myBool as id (void pointer) although [myBool class] prints __NSCFBoolean. For example this explains [myBool boolValue] == nil because id has no method boolValue.– vadian
Nov 23 '18 at 11:20
Most of the confusion is caused by the fact that the compiler treats
myBool as id (void pointer) although [myBool class] prints __NSCFBoolean. For example this explains [myBool boolValue] == nil because id has no method boolValue.– vadian
Nov 23 '18 at 11:20
2
2
And
> p [myBool boolValue] returns what? Be careful with po, since it's object, if it' 0, often it prints nil instead of false or 0 as you expect, use p when it's the case for check.– Larme
Nov 23 '18 at 13:49
And
> p [myBool boolValue] returns what? Be careful with po, since it's object, if it' 0, often it prints nil instead of false or 0 as you expect, use p when it's the case for check.– Larme
Nov 23 '18 at 13:49
__NSCFBoolean is returned from @NO, @YES, [NSNumber numberWithBool:NO] and [NSNumber numberWithBool:YES].– Willeke
Nov 24 '18 at 1:42
__NSCFBoolean is returned from @NO, @YES, [NSNumber numberWithBool:NO] and [NSNumber numberWithBool:YES].– Willeke
Nov 24 '18 at 1:42
@Vadian id is not the same as void pointer, see What is the meaning of id?.
[myBool boolValue] will send selector boolValue to myBool, how myBool is declared doesn't matter. The superclass of __NSCFBoolean is NSNumber and [myBool boolValue] == nil because [myBool boolValue] returns NO which po (print object) will print as <nil>.– Willeke
Nov 24 '18 at 2:00
@Vadian id is not the same as void pointer, see What is the meaning of id?.
[myBool boolValue] will send selector boolValue to myBool, how myBool is declared doesn't matter. The superclass of __NSCFBoolean is NSNumber and [myBool boolValue] == nil because [myBool boolValue] returns NO which po (print object) will print as <nil>.– Willeke
Nov 24 '18 at 2:00
add a comment |
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2
Most of the confusion is caused by the fact that the compiler treats
myBoolasid(void pointer) although[myBool class]prints__NSCFBoolean. For example this explains[myBool boolValue]==nilbecauseidhas no methodboolValue.– vadian
Nov 23 '18 at 11:20
2
And
> p [myBool boolValue]returns what? Be careful withpo, since it's object, if it' 0, often it prints nil instead of false or 0 as you expect, usepwhen it's the case for check.– Larme
Nov 23 '18 at 13:49
__NSCFBooleanis returned from@NO,@YES,[NSNumber numberWithBool:NO]and[NSNumber numberWithBool:YES].– Willeke
Nov 24 '18 at 1:42
@Vadian id is not the same as void pointer, see What is the meaning of id?.
[myBool boolValue]will send selectorboolValuetomyBool, howmyBoolis declared doesn't matter. The superclass of__NSCFBooleanisNSNumberand[myBool boolValue]==nilbecause[myBool boolValue]returnsNOwhichpo(print object) will print as<nil>.– Willeke
Nov 24 '18 at 2:00