The complexity argument is just not true. You do have to know this stuff in c++, you run into it all the time.
I wish I didn’t have to know about std::launder but I do
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I wish I didn’t have to know about std::launder but I do
Before C++ added it we relied on undefined behavior that the compilers agreed to interpret in the necessary way if and only if you made the right incantations. I’ve seen bugs in the wild because developers got the incantations wrong. std::launder makes it explicit.
For the broader audience because I see a lot of code that gets this wrong, std::launder does not generate code. It is a compiler barrier that blocks constant folding optimizations of specific in-memory constants at the point of invocation. It tells the compiler that the constant it believes lives at a memory address has been modified by an external process. In a C++ context, these are typically restricted to variables labeled ‘const’.
This mostly only occurs in a way that confuses the compiler if you are doing direct I/O into the process address space. Unless you are a low-level systems developer it is unlikely to affect you.
> Unless you are a low-level systems developer it is unlikely to affect you.
Making new data structure is common. Serializing classes into buffers is common.
std::launder is a tool for object instances that magically appear where other object instances previously existed but are not visible to the compiler. The typical case is some kind of DMA like direct I/O. The compiler can’t see this at compile time and therefore assumes it can’t happen. std::launder informs the compiler that some things it believes to be constant are no longer true and it needs to update its priors.
Std::vector needs launder.