Non-recursive maxSizeOf

[H. S. Teoh]

On Thursday, 6 August 2020 at 00:58:39 UTC, Per Nordlöw wrote:
> Is it possible to implement
>
> template maxSizeOf(T...)
> {
>     static if (T.length == 1)
>         enum size_t maxSizeOf = T[0].sizeof;
>     else
>     {
>         enum size_t firstSize = T[0].sizeof;
>         enum size_t maxSizeRest = maxSizeOf!(T[1 .. $]);
>         enum size_t maxSizeOf = firstSize >= maxSizeRest ? 
> firstSize : maxSizeRest;
>     }
> }
>
> in a non-recursive way?

Of course. In fact, it's trivial:

------
template maxSizeOf(T...)
{
	align(1) union Impl {
		T t;
	}
	enum maxSizeOf = Impl.sizeof;
}
------

To check that this does what we expect:
------
pragma(msg, maxSizeOf!(char)); // 1LU
pragma(msg, maxSizeOf!(char, short, ubyte)); // 2LU
pragma(msg, maxSizeOf!(char, long, ubyte)); // 8LU

align(1) struct S {
	long l;
	ubyte b;
}
pragma(msg, maxSizeOf!(long, S)); // 9LU
pragma(msg, maxSizeOf!(int, ubyte[7])); // 7LU
pragma(msg, maxSizeOf!(int, ubyte[3])); // 4LU
------

Why bother with recursion and all of that fancy gobbledygook when 
the compiler already knows how to compute the maximum size of 
something? ;-)