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POReasons not to use _Bool in Objective-C?
 

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  1. POReasons not to use _Bool in Objective-C?
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    <p>Since C99, C now has a proper Boolean type, <code>_Bool</code>. Objective-C, as a strict superset of C, inherits this, but when it was created back in the 1980s, there was no C Boolean type, so Objective-C defined <code>BOOL</code> as <code>signed char</code>.</p> <p>All of Cocoa uses <code>BOOL</code>, as does all non-NeXT/Apple Cocoa code that I've seen. Obviously, for compatibility with existing protocols (e.g., <code>-applicationShouldTerminateAfterLastWindowClosed:</code> from <code>NSApplicationDelegate</code>), matching the already-declared type is preferable, if for no other reason than to avert a warning.</p> <p>For cleanliness/readability purposes, <code>stdbool.h</code> defines <code>bool</code> as a synonym for <code>_Bool</code>, so those of us who don't want unnecessary underscores in our code can use that.</p> <p>Three other useful notes:</p> <ul> <li><code>@encode(_Bool)</code> evaluates to <code>"B"</code>. (<code>@encode(BOOL)</code> evaluates to <code>"c"</code>, for <code>signed char</code>.)</li> <li><code>sizeof(_Bool)</code> evaluates to <code>1</code>, which follows from C99's definition that <code>_Bool</code> is only as large as necessary to hold its two possible values. (<strong>Edit:</strong> Actually, the standard says only that it must be “large enough” to hold those two values; it does not place an upper bound, and, in fact, <a href="http://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/LowLevelABI/100-32-bit_PowerPC_Function_Calling_Conventions/32bitPowerPC.html#//apple_ref/doc/uid/TP40002438-SW21" rel="noreferrer">Mac OS X on 32-bit PowerPC defines it as 4 bytes.</a> Size difference is another thing to file under possible <code>BOOL</code>-vs.-<code>bool</code> compatibility issues.)</li> <li>On that note, the only two possible values of a <code>_Bool</code> are 1 and 0. Any other values are converted to one of these on assignment, as if you had done a double-negation (<code>!!</code>) or tested inequality against 0 (<code>!= 0</code>). The only ways to get a <code>_Bool</code> with some other value are the usual magicks: Pointer aliasing and unions.</li> </ul> <p>Is there any reason not to use <code>_Bool</code>/<code>bool</code> in new code?</p>
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    1. USPeter Hosey
    1. USPeter Hosey
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      1. POReasons not to use _Bool in Objective-C?
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      1. POReasons not to use _Bool in Objective-C?
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    1. COObjective-C isn't a 'strict superset of C' it is a 'a strict superset of a *particular* C' and is likely closely associated with the particular Objective-C version being targeted... anyway, ramble aside: Objective-C is also about conventions and for a particular environment / set of environments (as pointed out in the question), `BOOL` *is* part of that convention. I wouldn't rock the ship but have no "proper" justification (e.g. any incompatibilities?).
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    2. COAlso, `sizeof(t)` returns the number of chars, not the number of bits so ... I am confused with that statement. (Assuming 8 bits/char, that's far more than a boolean value requires).
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    3. COIt's a strict superset of whatever C you pick: C89, C99, or the GNU extensions thereof. To the extent that compiler-specific C extensions that aren't part of Objective-C are present, they will be whether you use (that compiler's) Objective-C or (that compiler's) plain C. And yes, it's the number of bytes (not necessarily octets); you can't have an object (by the C meaning of the term) smaller than a single byte. The closest you can get is structure members defined as some number of bits long, but even then, the implementation may/will round up as it sees fit.
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      1. POReasons not to use _Bool in Objective-C?
      1. USPeter Hosey
 

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