Entering dmd -preview=h shows this list:

  =all              list information on all upcoming language changes
  =dip25            implement [..] (Sealed references)
  =dip1000          implement [..] (Scoped Pointers)
  =dip1008          implement [..] (@nogc Throwable)
  =dip1021          implement [..] (Mutable function arguments)
  =fieldwise        use fieldwise comparisons for struct equality
  =markdown         enable Markdown replacements in Ddoc
  =fixAliasThis     when a symbol is resolved, check alias this scope before going to upper scopes
  =intpromote       fix integral promotions for unary + - ~ operators
  =dtorfields       destruct fields of partially constructed objects
  =rvaluerefparam   enable rvalue arguments to ref parameters
  =nosharedaccess   disable access to shared memory objects
  =in               in means scope const

While "implement <DIP link omitted>" do link to documents explaining details, I have no idea what `rvaluerefparam` does exactly. Is there an (online) resource where details to the others are given or linked?

On Saturday, 20 June 2020 at 14:36:25 UTC, Q. Schroll wrote:

> While "implement <DIP link omitted>" do link to documents explaining details, I have no idea what `rvaluerefparam` does exactly. Is there an (online) resource where details to the others are given or linked?

Ostensibly, it should enable binding of rvalues (temporaries) as ref arguments for functions (a-la how in C++ temporaries bind to const T&), i.e.

Tea makeSomeTea() { /* ... */ }

void takeSomeTea(ref const Tea) { /* ... */ }

void main()
{
    takeSomeTea(makeSomeTea());
}

Without that switch, the above won't compile, because historically D disallowed such binding. Manu (among others) pushed for this to be possible, hence the switch. Though implementation, AFAICT, is still somewhere in the "under construction" territory, judging by Bugzilla.