Re: enumerateObjectsWithOptions:usingBlock - runtime error "incorrect signature"

[David Chisnall]

> On 27 Nov 2017, at 17:25, Tom Sheffler <tom.sheffler@gmail.com> wrote:
> 
> I have the following code
> 
>   [mutarray enumerateObjectsWithOptions:NSEnumerationReverse 
> usingBlock:^(NSObject *o, NSUInteger idx, BOOL *stop) {
>     ...}];
> 
> This compiles and runs fine on one installation of gnustep on Ubuntu16, but 
> on a different installation, I get the following runtime error:
> 
> Calling [GSMutableArray -enumerateObjectsWithOptions:usingBlock:] with 
> incorrect signature.  Method has v32@0:8Q16^{?=^vii^?}24, selector has 
> v32@0:8Q16@?24
> 
> I believe my failing installation has an older version of gnustep-base.  Both 
> use clang 3.8.0-2ubuntu4.  Both installations of gnustep are from git repos.  
> I believe the failing one is an older installation, so I am not very 
> concerned about it.  But I am wary.
> 
> Has anyone else seen this?  I tried modifying the block in a number of ways, 
> and couldn’t find an incantation that worked.

It looks as if the caller knows that this is a block (encoding: @?), but the 
callee is not block aware.  If GNUstep is compiled by a compiler without blocks 
support, then it falls back to declaring the methods taking a pointer to a 
block structure and calling them by manually dereferencing the field that 
contains the invoke function.

There’s nothing to worry about here, unless you want to override the 
enumerateObjectsWithOptions:usingBlock: method in a subclass, at which point 
you’ll have some surprising behaviour!

Recompiling GNUstep-base with clang (possibly including rerunning configure if 
this is a configure-time check) should make this go away.

David