template: only static data member templates are allowed

Question

class value {
    template<typename T> T value_1;
    float value_2;

public:
    template<typename T> void Set1(T first) {
        value_2 = (float)0;
        value_1 = first;
    }

    void Set2(float second) {
        value_2 = second;
    }

    float Get2() {
        return this->value_2;
    }

    template<typename T> T Get1() {
        return value_1;
    }
};

Value_1 gives out an error, saying that only static data member templates are allowed. Is there a way to keep value_1 without a type?

Think about this: How would you be able to create an object of this class if `T` is not known? It's not possible. One solution is to make the whole class a template. — Some programmer dude, Feb 01 '18 at 17:31

score 6 · Accepted Answer · answered Feb 01 '18 at 17:31

The type of a non-static data member must be known. Otherwise, what's sizeof(value)?

To store a value of an arbitrary type, you can use std::any or boost::any.

Use:

class value {
    std::any value_1;
    float value_2;

public:
    template<typename T> void Set1(T first) {
        value_2 = (float)0;
        value_1 = first;
    }

    void Set2(float second) {
        value_2 = second;
    }

    float Get2() {
        return this->value_2;
    }

    template<typename T> T Get1() {
        return std::any_cast<T>(value_1);
    }
};

template: only static data member templates are allowed

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