On 09/21/2017 08:44 PM, David Zhang wrote:
Given the function F, where: F(Args...)(Args args) { ... }
How can I statically determine the size of the argument list in bytes?
Preferably, I would like a one-liner. However, std.algorithm doesn't
seem to support tuples, or `Args.each!(T => T.sizeof).sum` would work.
For the moment, I've settled on using a helper function:
size_t size(Args...)()
{
size_t size;
foreach(Arg; Args)
size += Arg.sizeof;
return size;
}
But it's a bit clunky. Is there a more idiomatic way to do this?
I don't have a one-liner, but here are some other solutions that might
be interesting. None of them is particularly pretty, though.
1) Recursive template:
----
template size_recur(Types ...)
{
static if (Types.length == 0) enum size_recur = 0;
else enum size_recur = Types[0].sizeof + size_recur!(Types[1 .. $]);
}
----
2) Using the std library:
----
template size_std(Types ...)
{
import std.algorithm: sum;
import std.range: only;
import std.meta: staticMap;
enum sizeOf(T) = T.sizeof;
enum size_std = staticMap!(sizeOf, Types).only.sum;
}
----
3) Declaring a packed struct in a function literal that gets immediately
called:
----
enum size_so_very_clever(Types ...) = () {
struct S { align(1) Types fields; }
return S.sizeof;
} ();
----
