/* * The 32-bit mach header appears at the very beginning of the object file for * 32-bit architectures. */ structmach_header { uint32_t magic; /* mach magic number identifier */ cpu_type_t cputype; /* cpu specifier */ cpu_subtype_t cpusubtype; /* machine specifier */ uint32_t filetype; /* type of file */ uint32_t ncmds; /* number of load commands */ uint32_t sizeofcmds; /* the size of all the load commands */ uint32_t flags; /* flags */ };
/* Constant for the magic field of the mach_header (32-bit architectures) */ #define MH_MAGIC 0xfeedface /* the mach magic number */ #define MH_CIGAM 0xcefaedfe /* NXSwapInt(MH_MAGIC) */
/* * The 64-bit mach header appears at the very beginning of object files for * 64-bit architectures. */ structmach_header_64 { uint32_t magic; /* mach magic number identifier */ cpu_type_t cputype; /* cpu specifier */ cpu_subtype_t cpusubtype; /* machine specifier */ uint32_t filetype; /* type of file */ uint32_t ncmds; /* number of load commands */ uint32_t sizeofcmds; /* the size of all the load commands */ uint32_t flags; /* flags */ uint32_t reserved; /* reserved */ };
/* Constant for the magic field of the mach_header_64 (64-bit architectures) */ #define MH_MAGIC_64 0xfeedfacf /* the 64-bit mach magic number */ #define MH_CIGAM_64 0xcffaedfe /* NXSwapInt(MH_MAGIC_64) */
/* * The 64-bit segment load command indicates that a part of this file is to be * mapped into a 64-bit task's address space. If the 64-bit segment has * sections then section_64 structures directly follow the 64-bit segment * command and their size is reflected in cmdsize. */ structsegment_command_64 {/* for 64-bit architectures */ uint32_t cmd; /* LC_SEGMENT_64 */ uint32_t cmdsize; /* includes sizeof section_64 structs */ char segname[16]; /* segment name */ uint64_t vmaddr; /* memory address of this segment */ uint64_t vmsize; /* memory size of this segment */ uint64_t fileoff; /* file offset of this segment */ uint64_t filesize; /* amount to map from the file */ vm_prot_t maxprot; /* maximum VM protection */ vm_prot_t initprot; /* initial VM protection */ uint32_t nsects; /* number of sections in segment */ uint32_t flags; /* flags */ };
/* * This is the symbol table entry structure for 64-bit architectures. */ structnlist_64 { union { uint32_t n_strx; /* index into the string table */ } n_un; uint8_t n_type; /* type flag, see below */ uint8_t n_sect; /* section number or NO_SECT */ uint16_t n_desc; /* see <mach-o/stab.h> */ uint64_t n_value; /* value of this symbol (or stab offset) */ };
在命令式编程中，这个表达式是计算 b 和 c 的和 a。假如之后 b 和 c 变化了，a 也不会变化。 而在响应式编程里，a 会随着 b 和 c 的变化而变化，不用再次执行这块代码求出一个值，再赋值给 a。 响应式编程可以简化交互式用户界面的开发，比如将视图与数据流绑定，数据流有新的值的时候，视图则会自动响应变化。 ReactiveX 是一组提供异步的数据流的 api，在 ReactiveX 的眼中，一切都可以当作数据流，我们可以用它来轻松的开始响应式编程。 而 RxSwift 就是 ReactiveX 的 Swift 实现。
