[fpc-devel] Blocks support

Jonas Maebe jonas.maebe at elis.ugent.be
Thu Jul 17 10:33:00 CEST 2014

On 16/07/14 23:21, Jonas Maebe wrote:
> On 16/07/14 21:19, Sven Barth wrote:
>> I'm not that sure whether using the same syntax is a good idea... people
>> want to have Delphi compatible anonymous functions which are basically
>> reference counted interfaces instead of records...
> Well, the block variable that's passed around is also a pointer. The
> record it points to can either be non-reference counted (in case it's a
> block for a global procedure/function, since those don't have context
> and hence can be reused for all instances) or reference counted. In the
> latter case, they start life on the stack, and are copied to the heap if
> necessary by the run time based on the copy/release calls that are
> made). In a sense, they behave a bit like an interface.

One definite incompatibility between blocks-based and other "reference 
to" functions right now is that the former do not accept types that are 
reference counted in Pascal. The reason is that when those blocks would 
be called from another language, the reference count wouldn't be 
updated. While other languages don't know about e.g. FPC-implemented 
ansistrings, some people would definitely start passing such ansistrings 
as pointers to outside code, so that this code could then pass it in 
again to a block invoked as a callback.


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