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Mutable Literals
#1 · March 23, 2022, 6:00 am
Posted by: kashmidheiser <kashmidheiser@...>
Reading this interesting article about Objective-C literals that we now have in FB:
I realized that literals are mutable without being initialized as such. (I was attempting to convert some JavaScript code to FB, and .js has a 'const' identifier which means it can't be reassigned, but its properties can be mutated. I was attempting to emulate that in FB.) Anywhere literals are used they're mutable. I inherently knew this, but I now look at literals in a new light.
I wrote the demo below as an exercise of the concept, and thought it might have limited interest on the list.
I've noted some anomalies between what's not supposed to work in Objective-C compared with what does work in FB. Also, note in the gConst_Arr that when the element "hot dog" is appended, it appears in quotes in the NSLog printed array. Something similar happens with localArray in fn MutateLocalLiterals. Any array element that does not contain alphanumeric characters is printed in quotes, thus the space in "hot dog" results in the quotes. Everybody but me probably knew that.
Ken
include "NSLog.incl"
begin globals
CFArrayRef gConst_Arr
CFDictionaryRef gConst_Dict
CFDictionaryRef gHeterogeneousDict
CFDictionaryRef gamesByReleaseYear
end globals
gConst_Arr = @[@"🍜", @"🍕", @"🍛", @"🍔", @"🍍"]
gConst_Dict = @{@"red": @"apple", @"yellow": @"banana", @"purple": @"grape"}
// This is supposed to fail because fn pow(2,2) is not a compile-time constant, but it works in FB.
gHeterogeneousDict = @{ @"key1": @"value1", @"key2": @2, @"key3": @(fn pow(10,2)) }
// This is supposed to fail because constant dictionaries can only have string keys, but it works in FB.
gamesByReleaseYear = @{@1985: @"Super Mario Bros", @1989: @"Prince of Persia", @1991: @"Lemmings"}
void local fn MutateGlobalLiterals
'~'1
NSLog( @"gConst_Arr before: %@n", gConst_Arr )
gConst_Arr = @[@"noodles", @"pizza", @"curry", @"hamburger", @"pineapple"]
NSLog( @"gConst_Arr after: %@n", gConst_Arr )
NSLog( @"gConst_Arr before: %@n", gConst_Dict )
gConst_Dict = @{@"red": @"cherry", @"yellow": @"lemon", @"purple": @"plum"}
NSLog( @"gConst_Arr after: %@n", gConst_Dict )
gConst_Arr = @[@"noodles", @"pizza", @"curry", @"hamburger", @"pineapple", @"spaghetti", @"hot dog"]
NSLog( @"gConst_Arr two new elements added: %@n", gConst_Arr )
gConst_Dict = @{@"red": @"cherry", @"yellow": @"lemon", @"purple": @"plum", @"orange": @"tangerine", @"green": @"watermelon"}
NSLog( @"gConst_Dict two new key-values added: %@n", gConst_Dict )
NSLog( @"gHeterogeneousDict: %@n", gHeterogeneousDict )
NSLog( @"gamesByReleaseYear: %@n", gamesByReleaseYear )
CFArrayRef limitedScopeControlArray = @[@"Alpha",@"Bravo",@"Charlie",@"Delta"]
NSLog( @"controlArray in scope of function: %@n", limitedScopeControlArray )
end fn
void local fn TestNewValues
'~'1
NSLog( @"gConst_Arr mutated: %@n", gConst_Arr )
NSLog( @"gConst_Dict mutated: %@n", gConst_Dict )
// Fails — not defined in global scope:
// NSLog( @"controlArray: %@n", limitedScopeControlArray )
end fn
void local fn MutateLocalLiterals
'~'1
CFArrayRef localArray = @[@"Toyota", @"Volkswagen", @"Daimler", @"Ford", @"Honda", @"BMW"]
NSLog( @"localArray: %@n", localArray )
localArray = @[@"Toyota", @"Volkswagen", @"Daimler", @"Ford", @"Honda", @"BMW", @"General Motors", @"Fiat Chrysler"]
NSLog( @"localArray mutated with new elements: %@n", localArray )
CFArrayRef quickAndDirtyMutableArray = @[]
NSLog( @"quickAndDirtyMutableArray: %@n", quickAndDirtyMutableArray )
quickAndDirtyMutableArray = @[@"Olivia", @"Emma", @"Ava", @"Charlotte", @"Sophia", @"Amelia", @"Isabella", @"Mia"]
NSLog( @"quickAndDirtyMutableArray: %@n", quickAndDirtyMutableArray )
end fn
fn MutateGlobalLiterals
fn TestNewValues
fn MutateLocalLiterals
HandleEvents
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