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Is there a way to have raw-types in (modern) C++?

 2 years ago
source link: https://dev.to/baenencalin/is-there-a-way-to-have-raw-types-in-modern-c-2knd
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Calin Baenen

Posted on Oct 24

Is there a way to have raw-types in (modern) C++?

What are "raw" types?

Raw types(in Java) is a type who has type-arguments (generics/templates*), but whose type-arguments are not specified in a declaration.
Consider the following (Java) code:

class NeverRaw1 {
    NeverRaw1(int i) { this.value = i; }
    int value;
}

class PossiblyRaw<T> {
    PossiblyRaw(T v) { this.value = v; }
    T value;
}

class NeverRaw2 extends PossiblyRaw<int> {
    NeverRaw2(int i) { this.value = i; }
}

// ... Some code later...

// This isn't raw because a type argument is specified.
PossiblyRaw<int> notRaw = new PossiblyRaw<>(10);
// This IS raw because none are specified
PossiblyRaw uncooked = new PossiblyRaw<int>(10);

// Invalid. Mismatched types.
notRaw = new PossiblyRaw<float>(10.56);
// Valid. No type mismatch because none is specified.
uncooked = new PossiblyRaw<float>(10.56);
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Why would you want types?

So, the first thought that probably popped into your head is "Hey. Isn't that not type-safe?", and to that, I say "Yes. It can be unsafe at times. But then it can also be utilized.".

So? Where can I use this?
Well, here's where I'm stuck. - I'm implementing a Token type for Janky, and I want to have a parse(std::string|char*) function that returns an array of Token.
How is this a problem?
It's a problem because even if you want to return an array of something, you must define the template arguments.
My Token type is written as such:

template<typename T, T v> struct Token {
    T              value = v;
    TokenType      type = TokenType::_UNASSIGNED;
    unsigned short col = 0;
    unsigned short ln = 0;
};
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And I can't create any abstraction, since all pieces of this structure are important to have. -- And because members aren't preserved when you say a piece of data is of its parent type.

So...

What's the best solution here?

Thanks!
Cheers!


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