@nogc with assoc array

[Jonathan Marler via Digitalmars-d-learn]

On Monday, 16 February 2015 at 19:12:45 UTC, FG wrote:
> Range violation is an Error, but never mind that. The real 
> question is: given all the work related to @nogc, wouldn't it 
> be better for such common Errors to be preallocated and only 
> have file and line updated when they are thrown?
>
> @nogc already, because they simply cast 
> typeid(OutOfMemoryError).init or 
> typeid(InvalidMemoryOperationError).init:
> extern (C) void onOutOfMemoryError(void* pretend_sideffect = 
> null) @trusted pure nothrow @nogc
> extern (C) void onInvalidMemoryOperationError(void* 
> pretend_sideffect = null) @trusted pure nothrow @nogc
>
> Could be made @nogc with one object of each kind preallocated:
> extern (C) void onAssertError( string file = __FILE__, size_t 
> line = __LINE__ ) nothrow
> extern (C) void onRangeError( string file = __FILE__, size_t 
> line = __LINE__ ) @safe pure nothrow
> extern (C) void onSwitchError( string file = __FILE__, size_t 
> line = __LINE__ ) @safe pure nothrow

This could be a good idea for some types of exceptions.  I 
believe OutOfMemory is already pre-allocated (it has to be since 
you can't allocate it once you are out of memory).  The problem 
with your suggestion is that if you allow the exception to be 
updated with the line number/filename(it isn't immutable), then 
you have to store it in TLS memory.  That may be an acceptable 
tradeoff, but you have to take that into consideration.  Also if 
you have a chain of exceptions you wouldn't be able to include 
the same exception more then once in the chain.

The problem D has with exceptions and GC memory is complex and 
will have different optimal solutions in different cases.  In 
some cases, it would be better for D to support non-GC heap 
allocated exceptions.  Maybe these types of exceptions could be 
derived from another class so the user code will know that the 
memory needs to be freed.  There are also other ideas but my 
point is we should make a plan about what solutions we think 
would be good to implement and determine which ones we want to 
tackle first.