CODEWITHSUNDEEP
c++smart-pointersexplicit
ofir agranat
ofir agranat

Reputation: 90

Smart Pointer with explicit constructor gets me an error

I'm trying to build my own Smart Pointer that will allow me to declare it like so:

SmartPtr<MyClass> ptr = new MyClass;

I want the constructor to be explicit so I made it like so:

template<class T>
class SmartPtr
{
public:
    SmartPtr();
    explicit SmartPtr(T* _ptr);
    explicit SmartPtr(const SmartPtr& other);
}

However, when I try to declare it as I mentioned on top, I get the following error:

error: conversion from ‘MyClass*’ to non-scalar type ‘SmartPtr<MyClass>’ requested

I know the error is because the copy CTOR has a special syntax with '=' and a conversion CTOR cannot be declared in that method. My question is, is there any method to keep the required syntax I mentioned above, and have an explicit CTOR?

Upvotes: 1

Views: 391

Answers (1)

Maxim Egorushkin
Maxim Egorushkin

Reputation: 136525

My question is, is there any method to keep the required syntax I mentioned above, and have an explicit CTOR?

Probably not. That syntax is copy initialization and it requires a non-explicit constructor.

Note that the copy constructor does not need to be explicit. If it is explicit then you won't be able to pass SmartPtr to a function that accepts it by value.

Another way to construct your pointer with minimum syntax overhead is to add a factory function and use it like:

template<class T> 
SmartPtr<T> make_ptr(T* p) { 
    return SmartPtr<T>{p}; 
}

auto ptr = make_ptr(new MyClass);

Or, something akin to std::make_shared<>:

auto ptr = make_ptr<MyClass>();

Upvotes: 1

Related Questions