@safe(bool)

[Nicholas Wilson via Digitalmars-d]

On Saturday, 19 August 2017 at 19:15:25 UTC, bitwise wrote:
> On Saturday, 19 August 2017 at 18:22:58 UTC, Guillaume Boucher 
> wrote:
>> 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:
>
> Those situations are not rare.
>
>> 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);
>> 	});
>> }
>
> Really?

With DIP 1012 you should be able to go

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

  	auto opSlice() @safeIf!safetyOn {
  		return Range(data, 0, data.length);
  	}
  }

  template safeIf(bool cond)
  {
      static if (cond) alias safeIf = AliasSeq!(safe);
      else                   alias safeIf = AliasSeq!();
  }

or even just

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

  	auto opSlice() @safetyOn {
  		return Range(data, 0, data.length);
  	}
  }

Container!int foo; // Container!(int, safe)
Container!(int, system) bar;

The only downside is that the second form leaves itself open to
Container!(int, trusted) quux;
which is probably undesirable.