default arguments for const ref parameters in extern C++ functions
geod24 at gmail.com
Tue Sep 15 01:48:07 UTC 2020
On Monday, 14 September 2020 at 18:58:44 UTC, 60rntogo wrote:
> On Monday, 14 September 2020 at 17:11:59 UTC, k2aj wrote:
>> AFAIK the only way to have default ref arguments is to use a
>> global variable:
>> extern(C++) struct Foo
>> int x;
>> immutable foo1 = Foo(1);
>> extern(C++) void fun(const ref Foo foo = foo1);
> Thanks. This appears to work, but feels like a hack. I can live
> with that, but I'm still wondering if there is a more idiomatic
> way of solving the problem.
D doesn't let rvalues bind to const ref (well, `in` will do that,
but it's D-only).
What was described as "global variable", is more of a "manifest
A (static) immutable variable with an initializer will always be
CTFE-d and available at compile time, so in this case it is
*exactly* what you need.
Also note that a default parameter doesn't affect the mangling /
ABI, because it works exclusively on the caller side. Thus, you
could just remove the default argument and your `extern(C++)`
binding would work just fine. But if you want to provide the same
API, `[static] immutable` + initializer is the way to go.
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