object-lifetime

How to deal with run-time parameters when using lifetime scoping?

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Autofac now supports this out of the box with an extension to the lifetime scopes. The BeginLifetimeScope() method has an overload that takes an Action<ContainerBuilder> that allows for adding new registrations specific to only that lifetime scope. So for the given example it would look something like: var builder = new ContainerBuilder(); builder.RegisterType<MyService>().As<IMyService>().InstancePerLifetimeScope(); var container … Read more

How can the type of braces influence object lifetime in C++?

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Gcc is correct. The lifetime of the temporary will be extended only when using list-initialization syntax (i.e. using braces) in initialization of an aggregate. (since C++20) a temporary bound to a reference in a reference element of an aggregate initialized using direct-initialization syntax (parentheses) as opposed to list-initialization syntax (braces) exists until the end of … Read more

What is the order of destruction of function arguments?

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I did not manage to find the answer in the standard, but I was able to test this on 3 most popular C++ compliant compilers. The answer of R Sahu pretty much explains that it is implementation defined. §5.2.2/8: The evaluations of the postfix expression and of the arguments are all unsequenced relative to one … Read more

Destruction of return value on destructor exception

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As per the standard this behavior is wrong and this has already been mentioned in the comments section of the question. This is stated in the section on Exception handling. As per the defect reports at open-std.org, they have been aware that implementations (GCC and Clang) were wrong about this as early as 2015-09-28. But … Read more

Lifetime of lambda objects in relation to function pointer conversion

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§5.1.2/6 says: The closure type for a lambda-expression with no lambda-capture has a public non-virtual non-explicit const conversion function to pointer to function having the same parameter and return types as the closure type’s function call operator. The value returned by this conversion function shall be the address of a function that, when invoked, has … Read more

Difference between IOptionsMonitor vs. IOptionsSnapshot

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IOptionsMonitor is a singleton service that retrieves current option values at any time, which is especially useful in singleton dependencies. IOptionsSnapshot is a scoped service and provides a snapshot of the options at the time the IOptionsSnapshot<T> object is constructed. Options snapshots are designed for use with transient and scoped dependencies. Use IOptions<T> when you … Read more

call to pure virtual function from base class constructor

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There are many articles that explain why you should never call virtual functions in constructor and destructor in C++. Take a look here and here for details what happens behind the scene during such calls. In short, objects are constructed from the base up to the derived. So when you try to call a virtual … Read more

Exact moment of “return” in a C++-function

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Due to Return Value Optimization (RVO), a destructor for std::string res in make_string_ok may not be called. The string object can be constructed on the caller’s side and the function may only initialize the value. The code will be equivalent to: void make_string_ok(std::string& res){ Writer w(res); } int main() { std::string res(“A”); make_string_ok(res); } That … Read more

Why would the behavior of std::memcpy be undefined for objects that are not TriviallyCopyable?

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Why would the behavior of std::memcpy itself be undefined when used with non-TriviallyCopyable objects? It’s not! However, once you copy the underlying bytes of one object of a non-trivially copyable type into another object of that type, the target object is not alive. We destroyed it by reusing its storage, and haven’t revitalized it by … Read more

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