Bindgen::Call::OutArgument

An out argument, see Parser::Method#out_arguments: the caller passes a pointer to a local variable, local, which the callee writes through. The prologue declares the local, before the call, and the epilogue hands its value back after it; either is nil where another part of the body does so, like the TupleResult of a Crystal wrapper. An in_out argument, a C++ reference, is initialized from the argument's value; an out-only one, a C++ pointer, isn't passed by the caller at all.