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From: Bhuyan, Jyotideep (JyotideepBhuyan_at_[hidden])
Date: 2023-10-01 05:14:53
This is strange ☹
By mistake, I removed the catch block from the example code. This was present in the original piece of code.
I am getting the compilation error with the new boost 1.82 and the VS2022 (v143 ) + C++17 is as follows at this line.
o << *boost::any_cast<T>(&a); //which was running with boost version 1.78 + VS2019 (v142) + C++14
Severity
Code
Description
Error
C2679
binary '<<': no operator found which takes a right-hand operand of type 'const ValueType' (or there is no acceptable conversion)
Best Regards,
Jyotideep (JD)
Confidential - Company Proprietary
From: Boost <boost-bounces_at_[hidden]> On Behalf Of Peter Dimov via Boost
Sent: Saturday, September 30, 2023 12:55 PM
To: boost_at_[hidden]
Cc: Peter Dimov <pdimov_at_[hidden]>
Subject: Re: [boost] boost::any_cast gives build errors with VS2022, boost v1.82 and C++17
Bhuyan, Jyotideep wrote: > Hi, > > I was using VS2019, boost v1. 78, and C++14 version and the below code was > working well. Same code gives build error with VS2022, boost v1. 82, and > C++17 due to "o << *boost: : any_cast<T>(&a);
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Bhuyan, Jyotideep wrote:
> Hi,
>
> I was using VS2019, boost v1.78, and C++14 version and the below code was
> working well. Same code gives build error with VS2022, boost v1.82, and
> C++17 due to "o << *boost::any_cast<T>(&a);
> " Instruction. I wanted to know why it behaves differently.
Your code compiles and works for me with VS2022 and C++17 (after adding
a `catch` clause after the `try`, e.g. https://urldefense.proofpoint.com/v2/url?u=https-3A__godbolt.org_z_eWv9sjYzz&d=DwICAg&c=9mghv0deYPYDGP-W745IEdQLV1kHpn4XJRvR6xMRXtA&r=nKjmvhl-FVZt-1iD5Ea7mULt--dNphU4qGuhbCJsO90&m=phs2270IlMJnrkY8KPgf3575O_9O78a6bb347nW4R28oRm_nFrGGqsw3BpqiTWZ4&s=hynNTB7tJ605xXLfaD7lhvL1xAyZ7JlB7RRwzxtQq0I&e=.)
What errors do you get?
> Code :
>
> class any_out
> {
> struct streamer
> {
> virtual void print(std::ostream& o, const boost::any& a) = 0;
> virtual streamer* clone() = 0;
> virtual ~streamer() {}
> };
>
> public:
> any_out() : m_streamer(nullptr)
> {
> }
>
> ~any_out()
> {
> delete m_streamer;
> }
>
> template <typename T> any_out(const T& value)
> : m_streamer(new streamer_imp<T>), m_object(value)
> {
> }
>
> any_out(const any_out& a)
> : m_streamer(a.m_streamer ? a.m_streamer->clone() : nullptr),
> m_object(a.m_object)
> {
> }
>
> template <typename T> any_out& operator=(const T& r)
> {
> any_out(r).swap(*this);
> return *this;
> }
>
> any_out& operator=(const any_out& r)
> {
> any_out(r).swap(*this);
> return *this;
> }
>
> any_out& swap(any_out& r) noexcept
> {
> std::swap(m_streamer, r.m_streamer);
> std::swap(m_object, r.m_object);
> return *this;
> }
>
> friend std::ostream& operator<<(std::ostream& o, const any_out& a)
> {
> if(a.m_streamer)
> {
> a.m_streamer->print(o, a.m_object);
> }
> return o;
> }
>
> boost::any& get() { return m_object; }
> const boost::any get()const { return m_object; }
> bool empty() const { return m_object.empty(); }
>
> private:
>
> template <typename T> struct streamer_imp : public streamer
> {
> virtual void print(std::ostream& o, const boost::any& a)
> {
> try {
> if (a.empty()) {
> o << "<empty>";
> }
> else {
> o << *boost::any_cast<T>(&a);
> }
>
> }
> }
> virtual streamer* clone()
> {
> return new streamer_imp<T>();
> }
> };
>
> // Members
> streamer* m_streamer;
> boost::any m_object;
>
> };
>
>
> I have migrated to VS2022, boost v1.82, and C++17, and due to a build error,
> I have changed the code below.
>
> virtual void print(std::ostream& o, const boost::any& a)
> {
> try {
> if (a.empty()) {
> o << "<empty>";
> }
> else {
> o << boost::any_cast<T*>(a);
> }
>
> }
> }
>
>
>
> any_out anyTest;
> anyTest = 100;
> std::string actualStr;
> actualStr = make_string() << anyTest;
>
> actualStr prints nullptr (0000000) instated of value 100 for VS2022, boost
> v1.82 and C++17
>
>
>
>
>
> Best Regards,
> Jyotideep (JD)
>
>
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