Arno Schoedl

The C++ rvalue lifetime disaster

Why do common C++ features like `std::min` and the ternary operator create dangling references? This talk reveals a fundamental language flaw and how to fix it.

The C++ rvalue lifetime disaster
#1about 3 minutes

The dual role of rvalue references in C++

Rvalue references were introduced for move semantics to avoid copies but are also used to manage the lifetime of temporary objects.

#2about 6 minutes

Why temporary lifetime extension fails in modern C++

The pre-C++11 feature for extending temporary object lifetimes does not work correctly with rvalue references, necessitating a custom macro to create a value or reference based on expression type.

#3about 6 minutes

How accessor methods cause rvalue amnesia

Standard accessor methods returning a const lvalue reference incorrectly bind to rvalues, losing critical lifetime information and leading to dangling references.

#4about 4 minutes

A proposal for fixing C++ reference binding rules

A proposed language fix using pragmas would introduce new, safer reference binding rules to prevent short-lived rvalues from binding to long-lived lvalue references.

#5about 3 minutes

Practical mitigations for rvalue lifetime issues today

Use custom macros to manage variable lifetimes, guard member accessors, and implement a correct ternary operator to work around the language's flawed binding rules.

#6about 1 minute

Managing C++ complexity with strong coding guidelines

The best way to manage the growing complexity of C++ is to establish strong internal coding guidelines and use custom libraries to standardize code patterns.

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