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Re: Listing markers in buffer


From: ian.tegebo
Subject: Re: Listing markers in buffer
Date: Thu, 02 Jun 2016 15:20:49 -0000
User-agent: G2/1.0

On Friday, April 29, 2016 at 10:13:27 AM UTC-7, Pascal J. Bourguignon wrote:
> "ian.tegebo" <address@hidden> writes:
> 
> > Looking at the C source, I can see that buffer to buffer_text structs
> > point to a singly linked list of Lisp_marker structs [...]
> 
> Markers belong to their owners, and it would be very dangerous if you
> could get them and set or reset them behind the back of their owners.

Could you provide an example?

Here's where I'm coming from:

While writing a yas-snippet, I wanted to modify previous text depending on some 
event within a field.  I found that by doing so, it broke because I didn't 
understand how overlays and markers were being used [1].  Naively, I thought I 
could get a list of markers in the buffer, like one can get the text properties 
and overlays for at least the purposes of learning/debugging.

Instead, I read the code to determine exactly what was going on.  In 
retrospect, I might have saved myself some time if I'd have been able to see 
the details of the markers in the affected region.  Now, I see where the 
markers are being held in yas-snippet, so I can still get at them and muck 
about.

When you say "dangerous", is it the same kind of danger I'm exposed to when 
changing the internal state elisp libraries *in general*?  Or do you mean 
"danger" in a specific sense, e.g. that some monstrous GC bug is hiding behind 
the scenes once a buffer's markers are exposed?

[1]: I'm aware that this is a known no-no


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