在 Class 定义 C++ 之前使用 Class 成员 Function 指针

Question

I have the following code:

// FILE_NAME: compiler.h

typedef enum Precedence { /* ENUM MEMBERS */ } Precedence;
typedef enum TokenType { /* ENUM MEMBERS */ } TokenType;

typedef void (Compiler::*ParseFn)();

typedef struct ParseRule {
    ParseFn prefix;
    ParseFn infix;
    Precedence precedence;
} ParseRule;

class Compiler {
    public:
        std::unordered_map<TokenType, ParseRule> rules;
        ParseRule getRule(TokenType type) {
            return rules[type];
        };
        void binary();
        void unary();
};

I am trying to define a hashmap that maps a key of TokenType to a value that has the form of the struct ParserRule .

An example of a key-value pair for the Compiler::rules hashmap is as follows:

rules[TOKEN_MINUS] = {unary, binary, PREC_TERM}

When I try to compile with C++11, I get the following error, plus many others:

./compiler/compiler.h:58:15: error: use of undeclared identifier 'Compiler'
typedef void (Compiler::*ParseFn)();

This makes sense since I am trying to use the class Compiler to define the type ParseFn before the Compiler class has been defined.

I am very new to coding in C/C++ (I started learning a couple of weeks ago), so I was wondering if there is another way of defining the types and classes without causing a compiler error.

Answer 1

You need to (pre-)declare Compiler as a class before referring to it:

class Compiler;

typedef void (Compiler::*ParseFn)();