trick to make throwing method @nogc

[Profile Anaysis via Digitalmars-d-learn]

On Saturday, 25 February 2017 at 19:59:29 UTC, ikod wrote:
> Hello,
>
> I have a method for range:
>
> struct Range {
>     immutable(ubyte[]) _buffer;
>     size_t             _pos;
>
>     @property void popFront() pure @safe {
>         enforce(_pos < _buffer.length, "popFront from empty 
> buffer");
>         _pos++;
>     }
> }
>
> I'd like to have @nogc here, but I can't because enforce() is 
> non- at nogc.
> I have a trick but not sure if it is valid, especially I don't 
> know if optimization will preserve code, used for throwing:
>
> import std.string;
>
> struct Range {
>     immutable(ubyte[]) _buffer;
>     size_t  _pos;
>
>     this(immutable(ubyte[]) s) {
>         _buffer = s;
>     }
>     @property void popFront() pure @safe @nogc {
>         if (_pos >= _buffer.length ) {
>             auto _ = _buffer[$]; // throws RangeError
>         }
>         _pos++;
>     }
> }
>
> void main() {
> 	auto r = Range("1".representation);
> 	r.popFront();
> 	r.popFront(); // throws
> }
>
> Is it ok to use it? Is there any better solution?
>
> Thanks!

You can wrap a gc function in a nogc call using a function 
pointer that casts it to a nogc. You do this first by casting to 
void* then back to the same signature as the function + @nogc. 
This "tricks" the compiler in to calling the gc function from a 
nogc function. The problem is, of course, it is not safe if the 
gc is turned off as it will result in a memory leak. This may or 
may not be an issue with enforce depending on if it allocates 
before or after the check.