@safe(bool)

[Guillaume Boucher via Digitalmars-d]

On Thursday, 17 August 2017 at 16:32:20 UTC, bitwise wrote:
> In a high-performance context though, the performance hit may 
> be unacceptable.

Well in those super rare situations, there's always the 
workaround with mixins:

mixin template funcWithAttr(string decl, string attributes, 
string code) {
     pragma(msg, "<<<" ~ code ~ ">>>");
     mixin(decl ~ attributes ~ "{" ~ code ~" }");
}

struct Container(T, bool safetyOn = true)
{
	static if(safe)
		RefCounted!(T[]) data;
	else
		T[] data;

	mixin funcWithAttr!("auto opSlice()", safetyOn ? "@safe" : "", q{
		return Range(data, 0, data.length);
	});
}