optional

高级C/C++编译技术之读书笔记（三）之动态库设计

由 拈花ヽ惹草 提交于 2020-12-30 04:33:56
　　最近有幸阅读了《高级C/C++编译技术》深受启发，该书深入浅出地讲解了构建过程（编译、链接）中的各种细节，从多个角度展示了程序与库文件或代码的集成方法，提出了面向代码复用和系统集成的软件架构设计方法，以及系统开发过程中疑难问题的解决方案。 　　以下将回头记录下其中的关键要点，以便后面查阅。 本节思维导图 1. 关于-fPIC编译器选项 1.1 -fPIC代表什么 　　“PIC”是位置无关代码（Position-independent Code）的缩写，说到位置无关代码，我们会立马想到加载重定位，加载重定位将动态库加载到进程内存空间中，但是只有第一次加载这个动态库的进程可以使用它，当其它进程需要加载同一动态库的时候，除了将动态库的完整副本加载到自身内存空间以外，别无他法，当更多的进程需要加载某一特定的动态库时，内存中会存在更多的副本。这种限制的根本原因在于加载过程设计的缺陷，在将动态库加载到进程中之前，装载器需要修改动态库的代码段，使得在加载该库的进程中，动态库的所有符号是有意义的，即便这种方法可以满足基本的运行需求，但其导致的最终结果是由于动态库代码的修改是不可逆的，因此其它进程难以直接复用这个已加载的动态库。 　　为了解决加载重定位的缺陷，重新设计加载机制，避免将加载的动态库代码段绑定到第一个加载该动态库的进程中，提出了PIC机制

How to parse json file with std::optional< std::variant > type in C++?

由 五迷三道 提交于 2020-12-30 04:20:53
问题 How can I parse nested json in c++? I am looking for a json parser that is capable of parsing nested json. Especially this field in the example json below: optional<variant<bool, Secondary>> secondary; It is type composition of optional and variant . Though only the full example can surface the problem in a clearer way, a minimal starting point example would be this one: [ {}, { "secondary": false }, { "secondary": { "chance": 10, "boosts": { "spd": -1 } } }, { "secondary": { "chance": 30,

How to parse json file with std::optional< std::variant > type in C++?

由 只谈情不闲聊 提交于 2020-12-30 04:06:31
问题 How can I parse nested json in c++? I am looking for a json parser that is capable of parsing nested json. Especially this field in the example json below: optional<variant<bool, Secondary>> secondary; It is type composition of optional and variant . Though only the full example can surface the problem in a clearer way, a minimal starting point example would be this one: [ {}, { "secondary": false }, { "secondary": { "chance": 10, "boosts": { "spd": -1 } } }, { "secondary": { "chance": 30,

How to parse json file with std::optional< std::variant > type in C++?

由 匆匆过客 提交于 2020-12-30 04:03:14
问题 How can I parse nested json in c++? I am looking for a json parser that is capable of parsing nested json. Especially this field in the example json below: optional<variant<bool, Secondary>> secondary; It is type composition of optional and variant . Though only the full example can surface the problem in a clearer way, a minimal starting point example would be this one: [ {}, { "secondary": false }, { "secondary": { "chance": 10, "boosts": { "spd": -1 } } }, { "secondary": { "chance": 30,

How to parse json file with std::optional< std::variant > type in C++?

由 折月煮酒 提交于 2020-12-30 04:01:33
问题 How can I parse nested json in c++? I am looking for a json parser that is capable of parsing nested json. Especially this field in the example json below: optional<variant<bool, Secondary>> secondary; It is type composition of optional and variant . Though only the full example can surface the problem in a clearer way, a minimal starting point example would be this one: [ {}, { "secondary": false }, { "secondary": { "chance": 10, "boosts": { "spd": -1 } } }, { "secondary": { "chance": 30,

Flattening a list of elements in Java 8 Optional pipeline

由 做~自己de王妃 提交于 2020-12-29 13:19:54
问题 I have a id value which can be null . Then I need to call some service with this id to get a list of trades and fetch the first not null trade from the list. Currently I have this working code Optional.ofNullable(id) .map(id -> service.findTrades(id)) .flatMap(t -> t.stream().filter(Objects::nonNull).findFirst()) .orElse(... default value...); Is it possible to implement a line with a flatMap call more elegantly? I don't want to put much logic in one pipeline step. Initially I expected to

Flattening a list of elements in Java 8 Optional pipeline

由 你说的曾经没有我的故事 提交于 2020-12-29 13:19:12
问题 I have a id value which can be null . Then I need to call some service with this id to get a list of trades and fetch the first not null trade from the list. Currently I have this working code Optional.ofNullable(id) .map(id -> service.findTrades(id)) .flatMap(t -> t.stream().filter(Objects::nonNull).findFirst()) .orElse(... default value...); Is it possible to implement a line with a flatMap call more elegantly? I don't want to put much logic in one pipeline step. Initially I expected to

Flattening a list of elements in Java 8 Optional pipeline

由 泪湿孤枕 提交于 2020-12-29 13:18:37
问题 I have a id value which can be null . Then I need to call some service with this id to get a list of trades and fetch the first not null trade from the list. Currently I have this working code Optional.ofNullable(id) .map(id -> service.findTrades(id)) .flatMap(t -> t.stream().filter(Objects::nonNull).findFirst()) .orElse(... default value...); Is it possible to implement a line with a flatMap call more elegantly? I don't want to put much logic in one pipeline step. Initially I expected to

Optional vs if/else-if performance java 8

由 ℡╲_俬逩灬. 提交于 2020-12-29 09:31:42
问题 Hello i have two samples of code if/else if/else statements private Object getObj(message) { if (message.getA() != null) return message.getA(); else if (message.getB() != null) return message.getB(); else if (message.getC() != null) return message.getC(); else return null; } Optional statements private Optional<Object> wrap(Object o){ return Optional.ofNullable(o); } private Object getObj(message) { return wrap(message.getA()) .orElseGet(() -> wrap(message.getB()) .orElseGet(() -> wrap

What is a clean way to convert a Result into an Option?

由 我的未来我决定 提交于 2020-12-29 08:49:16
问题 Before updating to a more recent Rust version the following used to work: fn example(val: &[&str]) { let parsed_value: Vec<usize> = val .iter() .filter_map(|e| e.parse::<usize>()) .collect(); } However, now the parse method returns a Result type instead of an Option and I get the error: error[E0308]: mismatched types --> src/lib.rs:4:25 | 4 | .filter_map(|e| e.parse::<usize>()) | ^^^^^^^^^^^^^^^^^^ expected enum `std::option::Option`, found enum `std::result::Result` | = note: expected type
订阅 optional