Re: 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-@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.