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Questions - variant

How to return const& from std::visit?

I have encountered what i consider to be a strange situation with std::visit and overloaded which is giving me a compiler error. To illustrate what i am trying to do I have an example using std::visit...
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kanoisa

c++

variant

Votes: 0

Answers: 1

Latest Answer

The default behavior when calling a lambda (or a function for that matter) is to have the value returned by copy. Since your lambda expressions that you pass to overloaded return by copy, binding a re...
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cigien

Is it possible for VariantClear to crash software if VariantInit is not called beforehand?

I have an exception that I cannot easily replicate, but I have a very strong suspicion that it happens during VariantClear(). I have a function that defines a variant and then passes it off to another...
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Farhät

windows

winapi

visual-c++

variant

Votes: 0

Answers: 1

Latest Answer

VariantClear checks the first 16 bits of the VARIANT to find the variant type. Depending on the type, VariantClear might call CoTaskMemFree or treat the variant as a COM pointer it calls Release on. I...
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Anders

c++ - valid use of CRTP std::variant with two elements, but no more

I'm trying to use CRTP with std::variant to achieve a classic Expression class, for example in some algebraic data type data Expr = Num Int | Add Expr Expr | Sub Expr Expr ... I use CR...
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farmerzhang1

c++

functional-programming

c++17

variant

crtp

Votes: 0

Answers: 1

Latest Answer

std::variant can't be used with incomplete types. When you have an inline definition of Add::eval_impl in the body of struct Add, Num is complete and Add is complete, but Sub hasn't been defined (whic...
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Artyer

A macro registering marked structures into an enum

I am searching for a macro, or a procedural macro, which could register some marked structures (or enums) as variants of an enum. Moreover, I would like, that if the marked structures are implementing...
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FreD

rust

enums

macros

variant

Votes: 0

Answers: 1

Latest Answer

First, you have no way of knowing how much structs are annotated with the attribute. So you have to pass this number for each invocation. The macro should cache the struct, and when that number is rea...
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Chayim Friedman

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