[英]What are the details of “Objective-C Literals” mentioned in the Xcode 4.4 release notes?
我正在浏览 Xcode 4.4 的发行说明并注意到这一点:
LLVM 4.0 编译器
Xcode 现在包含 Apple LLVM 编译器 4.0 版,包括以下新的Objective-C 语言特性:[...]
- Objective-C 文字:为 NSArray、NSDictionary 和 NSNumber 创建文字,与 NSString 的文字相同
我对这个功能很感兴趣。 我并不完全清楚NSString
文字是如何工作的,以及如何在NSArray
、 NSDictionary
和NSNumber
上使用它们。
详情是什么?
从http://cocoaheads.tumblr.com/post/17757846453/objective-c-literals-for-nsdictionary-nsarray-and逐字复制:
Objective-C 文字:现在可以为 NSArray、NSDictionary 和 NSNumber 创建文字(就像可以为 NSString 创建文字一样)
之前:
array = [NSArray arrayWithObjects:a, b, c, nil];
现在:
array = @[ a, b, c ];
之前:
dict = [NSDictionary dictionaryWithObjects:@[o1, o2, o3]
forKeys:@[k1, k2, k3]];
现在:
dict = @{ k1 : o1, k2 : o2, k3 : o3 };
之前:
NSNumber *number;
number = [NSNumber numberWithChar:'X'];
number = [NSNumber numberWithInt:12345];
number = [NSNumber numberWithUnsignedLong:12345ul];
number = [NSNumber numberWithLongLong:12345ll];
number = [NSNumber numberWithFloat:123.45f];
number = [NSNumber numberWithDouble:123.45];
number = [NSNumber numberWithBool:YES];
现在:
NSNumber *number;
number = @'X';
number = @12345;
number = @12345ul;
number = @12345ll;
number = @123.45f;
number = @123.45;
number = @YES;
[编辑]
http://news.ycombinator.com/item?id=3672744上的zxoq添加了更多有趣的新下标。 (添加文字):
arr[1] === [arr objectAtIndex:1]
dict[@"key"] === [dict objectForKey:@"key"]
[编辑 2]
在多个WWDC 2012会议中讨论了新的 ObjC 文字。 我故意没有删除每张幻灯片的文件名和时间,以便您可以根据需要自己找到它们。 它们与本文中所述的内容基本相同,但我还将在图片上方提及一些新内容。
请注意,图像都是大的。 只需将它们拖到另一个选项卡中即可以原始大小查看它们
[NSNumber numberWithint:42]
[NSNumber numberWithDouble:10.8]
[NSNumber numberWithBool:YES]
[NSNumber numberWithint:6 + x * 2012]
@42
@10.8
@YES
@(6 + x * 2012)
[NSArray arrayWithObjects: a, b, c, nil]
[array objectAtIndex:i]
[NSDictionary dictionaryWithObjectsAndKeys: v1, k1, v2, k2, nil];
[dictionary valueForKey:k]
@[a, b, c]
array[i]
@{k1:v1, k2:v2}
dictionary[k]
当你有一个表达式(例如M_PI / 16
)时,你应该把它放在括号里。
此语法适用于数字表达式、布尔值、在 (C-) 字符串中查找索引、布尔值、枚举常量甚至字符串!
NSNumber *piOverSixteen = [NSNumber numberWithDouble: (M_PI / 16)];
NSNumber *hexDigit = [NSNumber numberWithChar:"0123456789ABCDEF"[i % 16]];
NSNumber *usesScreenFonts = [NSNumber numberWithBool:[NSLayoutManager usesScreenFonts]];
NSNumber *writingDirection = [NSNumber numberWithInt:NSWritingDirectionLeftToRight];
NSNumber *path = [NSString stringWithUTF8String: getenv("PATH")];
NSNumber *piOverSixteen = @( M_PI / 16 );
NSNumber *hexDigit = @( "0123456789ABCDEF"[i % 16] );
NSNumber *usesScreenFonts = @( [NSLayoutManager usesScreenFonts] );
NSNumber *writingDirection = @( NSWritingDirectionLeftToRight );
NSNumber *path = @( getenv("PATH") );
有关字符串以及如何/何时使用此文字语法的更多信息:
NSString *path = [NSString stringWithUTF8String: getenv("PATH")];
for (NSString *dir in [path componentsSeparatedByString: @":"]) {
// search for a file in dir...
}
NSString *path = @( getenv("PATH") );
for (NSString *dir in [path componentsSeparatedByString: @":"]) {
// search for a file in dir...
}
// when you write this:
array = @[a, b, c ];
// compiler generates:
id objects[] = { a, b, c };
NSUInteger count = sizeof(objects) / sizeof(id);
array = [NSArray arrayWithObjects:objects count:count];
// when you write this:
dict = @{k1 : o1, k2 : o2, k3 : o3 };
// compiler generates:
id objects[] = { o1, o2, o3 };
id keys[] = { k1, k2, k3 };
NSUInteger count = sizeof(objects) / sizeof(id);
dict = [NSDictionary dictionaryWithObjects:objects
forKeys:keys
count:count];
@implementation SongList {
NSMutableArray *_songs;
}
- (Song *)replaceSong:(Song *)newSong atindex:(NSUinteger)idx {
Song *oldSong = [_songs objectAtIndex:idx];
[_songs replaceObjectAtindex:idx withObject:newSong];
return oldSong;
}
@implementation SongList {
NSMutableArray *_songs;
}
- (Song *)replaceSong:(Song *)newSong atindex:(NSUinteger)idx {
Song *oldSong = _songs[idx];
_songs[idx] = newSong;
return oldSong;
}
@implementation Database {
NSMutableDictionary *_storage;
}
- (id)replaceObject:(id)newObject forKey:(id <NSCopying>)key {
id oldObject = [_storage objectForKey:key];
[_storage setObject:object forKey:key];
return oldObject;
}
@implementation Database {
NSMutableDictionary *_storage;
}
- (id)replaceObject:(id)newObject forKey:(id <NSCopying>)key {
id oldObject = _storage[key];
_storage[key] = newObject;
return oldObject;
}
[编辑 3]
Mike Ash有一篇关于这些新文字的精彩文章。 如果您想了解更多有关这些内容的信息,请务必查看。
Objective-C 编译器具有NSConstantString
类实例的内存布局的硬编码知识,也就是__CFConstantString
类。 查看 clang 源代码中lib/Rewrite/RewriteModernObjC.cpp
中的RewriteObjCStringLiteral
函数。 编译器只是发出与NSConstantString
类的实例布局匹配的数据。
文字NSArray
和NSDictionary
实例有几种可能性。 他们可以做一些类似于他们对文字字符串所做的事情 - 在编译器中硬编码实例布局(对于特殊子类)并在该布局中发出数据。 或者他们可以让编译器发出代码,在运行时简单地创建一个实例。
1) NSNumber
、 NSDictionary
和NSArray
文字在Xcode 4.4中可用。
2) NSDictionary
和NSArray
下标需要“ Xcode 4.4 and OS X 10.8 or later SDK ”或“ Xcode 4.5 and iOS 6 or later SDK ”
在我看来,下标需要运行时支持,因此在iOS6之前不起作用。
Apple LLVM Compiler 4.0 添加了对 Objective-C 的字面支持。 它从at sign
@
开始
NSNumber 字面量
NSNumber *someBool = [NSNumber numberWithBool:YES];
//BOOL literal
NSNumber *someBool = @YES;
NSNumber *someChar= [NSNumber numberWithChar:'a'];
//character literal
NSNumber *someChar = @'a';
NSNumber *someInt = [NSNumber numberWithInt:1];
NSNumber *someInt = [NSNumber numberWithUnsignedInt:1U];
NSNumber *someInt = [NSNumber numberWithLong:1L];
NSNumber *someInt = [NSNumber numberWithLongLong:1LL];
//integer literal
NSNumber *someInt = @1;
NSNumber *someInt = @1U;
NSNumber *someInt = @1L;
NSNumber *someInt = @1LL;
NSNumber *someFloat = [NSNumber numberWithFloat:3.141592654F];
NSNumber *someFloat = [NSNumber numberWithDouble:3.1415926535];
//float literal
NSNumber *someFloat = @3.141592654F;
NSNumber *someFloat = @3.1415926535;
集合文字
NSArray *someArray = [NSArray arrayWithObjects: @"A", @"B", @"C", nil];
//array literal
NSArray *someArray = @[ @"A", @"B", @"C" ];
NSDictionary *someDict = [NSDictionary dictionaryWithObjectsAndKeys:
@"key1", @"value1",
@"key1", @"value2",
nil];
//dictionary literal
NSDictionary *someDict = @{ @"Character" : @"Zelda",
@"key1" : @"value2",
@"key2" : @value2 };
集合下标
NSString *var1 = [someArray objectAtIndex:0]; // Returns 'A'
NSString *var2 = [someDict objectForKey:@"key1"]; // Returns 'value1'
//Collection Subscripting
//read
NSString *var1 = someArray[0]; // Returns 'A'
NSString *var2 = someDict[@"key1"]; // Returns 'value1'
//write to mutable collection
someArray[0] = @"AA";
someDict[@"key1"] = @"value11";
Boxed Expressions - 将 C 风格的表达式转换为 Objective-C。 适用于数字、枚举、结构
//Syntax @( <expression> )
[NSNumber numberWithInt:(INT_MAX + 1)];
//Boxed Expressions
NSNumber *var = @(INT_MAX + 1);
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