Question

I m 为汇编者撰写前端,目前正在实施校正仪扫描功能。我将使用<代码>Punctuator等舱,代表我方的输入源文档中的教员,此外,它也是一些静态扫描方法的所在地。这里是辅导员。

#ifndef PUNCTUATOR_H_
#define PUNCTUATOR_H_

#include <string>
#include <unordered_map>
#include <unordered_set>
#include <string>

#include "reserved_component.h"

enum class PunctuatorEnum {
    OPEN_BRACE,
    CLOSE_BRACE,
    TERMINATOR,
    EQUAL,
    PLUS,
    MINUS,
    MULTIPLY,
    DIVIDE,
};

class Punctuator : public ReservedComponent {
public:
    Punctuator(std::string lexeme);
    Punctuator(Punctuator&& punctuator);

    static bool IsPunctuator(std::string buffer);
    static PunctuatorEnum ForLexeme(std::string buffer);

private:
    PunctuatorEnum punctuator_enum;
    static std::unordered_map<std::string, PunctuatorEnum> dictionary;
};

#endif // PUNCTUATOR_H_

由于你能够使用静态<代码>unordered_map,储存可能的旁听器的“字典”,然后使用该地图检查某一方的护卫是否代表旁人。我将地图放在旁边,c 在这里:

#include "punctuator.h"

std::unordered_map<std::string, PunctuatorEnum> Punctuator::dictionary = {
    { "{", PunctuatorEnum::OPEN_BRACE },
    { "}", PunctuatorEnum::CLOSE_BRACE },
    { ".", PunctuatorEnum::TERMINATOR },
    { "=", PunctuatorEnum::EQUAL },
    { "+", PunctuatorEnum::PLUS },
    { "-", PunctuatorEnum::MINUS },
    { "*", PunctuatorEnum::MULTIPLY },
    { "/", PunctuatorEnum::DIVIDE }
};

Punctuator::Punctuator(std::string lexeme) : ReservedComponent(lexeme) {
    this->punctuator_enum = dictionary.at(lexeme);
}

Punctuator::Punctuator(Punctuator&& punctuator) : ReservedComponent(std::move(punctuator)) {
    this->punctuator_enum = std::move(punctuator.punctuator_enum);
}

bool Punctuator::IsPunctuator(std::string buffer) {
    return dictionary.contains(buffer);
}

PunctuatorEnum Punctuator::ForLexeme(std::string lexeme) {
    return dictionary.at(lexeme);
}

I understand this is not the cleanest approach as this forces me to maintain the PunctuatorEnum and the unordered map, but it s what I ve chosen so far. I d also like to implement a method StartsPunctuator(char c) to check whether a given char starts a punctuator.

My question is as follows: Is it possible to declare a static unordered_set variable in my Punctuator class, say punctuator_first_char, and have it initialized to store only the first chars of every entry of the key-set of the static member variable dictionary? This way I would be able to simply call the contains method on punctuator_first_char in my StartsPunctuator(char ch) method without having to iterate through dictionary.

Answer 1

能否在我的<代码>Punctuator类别上宣布static unordered_setps, 说punctuator_first_char/code>, 是否初步将其储存在固定成员变量的关键条目-dictionary 上的每一条目中的第一个焦炭?


是:
#include <unordered_set> 

class Punctuator : public ReservedComponent {
   //...
private:
    PunctuatorEnum punctuator_enum;
    static std::unordered_map<std::string, PunctuatorEnum> dictionary;
    static std::unordered_set<char> punctuator_first_char;
};

初始:
#include <algorithm> // std::transform
#include <iterator>  // std::inserter

std::unordered_map<std::string, PunctuatorEnum> Punctuator::dictionary = { ... };

std::unordered_set<char> Punctuator::punctuator_first_char = [] {
    std::unordered_set<char> rv;
    std::transform(dictionary.begin(), dictionary.end(),
                   std::inserter(rv, rv.end()),
                   [](auto&& str_punctenum) { return str_punctenum.first[0]; });
    return rv;
}();

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