The distinction and use of nullable,nonnull, null_resettable and _null_unspecified

1. Keywords: can be used in attribute methods and return value parameters

Keyword action: Hint function tells developer property information

Purpose of the keyword: to cater to Swift's strong language, Swift must specify whether an object is empty

Keyword Benefits: Improve code planning and reduce communication costs

Just provide a warning and do not report a compilation error

Nullabel effect: Hint may be empty

Syntax 1

@property (Nonatomic, Strong, Nullabel) NSString * name;

Syntax 2

@property (nonatomic, Strong) NSString * _nullabel name;

Syntax 2

@property (nonatomic, Strong) NSString * __nullabel name;

nonnull function: Hint cannot be empty

Syntax 1

@property (Nonatomic, Strong, nonnull) NSString * name;

Syntax 2

@property (nonatomic, Strong) NSString * _nonnull name;

Syntax 2

@property (nonatomic, Strong) NSString * __nonnull name;

null_resettable function: a condition that must be handled as empty get cannot return nil set method can be passed to null

Overriding the Get method

@property (nonatomic, strong,null_resettable) nsstring * name;

You can't use grammar 2 to make an error.

_null_unspecified: Not sure whether it is empty

Rarely used

—————————

!_view change to _view = nil Because Swift does not support the former

Supplement the default between macros (Ns_assume_nonull_begin/end) is nonnull strong

Keyword cannot be used for basic data types

************************************************************************************

2. Generics

Why quit generics? cater to Swift

Generic benefits: 1. Restriction type 2. Improve code specifications reduce communication costs

Generic usage: Type < restriction type >

Generics are just news alerts

Generic benefits are removed from the array to use point syntax

Hints for adding elements to an array

Usage scenarios for generics in development: 1. To restrict collection types

The distinction and use of nullable,nonnull, null_resettable and _null_unspecified