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Re: Skeleton angle brackets '<' and '>'


From: B.V. Raghav
Subject: Re: Skeleton angle brackets '<' and '>'
Date: Sat, 09 Jan 2016 00:03:45 +0530
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Alan Mackenzie <address@hidden> writes:

> B.V. Raghav <address@hidden> wrote:
>> Hi,
>
>> There are smart tools for the purpose, but I prefer to stick to the old
>> school for auto pairing.
>
>> Electric Pair mode and Skeleton pair, like this:
>> (electric-pair-mode t)
>> (setq skeleton-pair t)
>
>> While in the c++ mode, (hopefully true for all c-modes)
>> I am able to successfully pair (), {}, and [], with a single key press,
>> i.e. of the preceding character of the pair.
>
>> I also want to pair the angle brackets, i.e. `<' and `>' characters.
>
> Be careful what you want!  Do you also want automatically to pair up
> "less than" with "greater than"?  It could get pretty tedious if, every
> time you wanted to write "i < 10", you got "i <>", forcing you to delete
> the ">" before writing in the "10".
>
> This overloading of < and > with two meanings (actually, three when you
> count "#include <stdio.h>", but that causes few problems) causes great
> difficulties for C++ Mode.  Only after extensive analysis can the mode
> determine that a < and a > are a pair of template delimiters, and even
> then, can't do it with 100% certainty.
>
> For example, how many parameters are passed to foo in the following:
>
>     foo (a < b, c > d);

Now I remember the problem. It was there when I simillarly, had to pass
a templated type as argumentn to preprocessors using typedefs. This
thread helped me recall.
http://stackoverflow.com/a/7304772/4366367

One of the examples, that extensively uses typedefs to avoid this
problem is Boost.Exceptions uses #define , template<> and overloading
operator << --- extensively
http://www.boost.org/doc/libs/1_60_0/libs/exception/doc/boost-exception.html

>
> ?  It might be a function call with two relational expressions, it might
> be a declaration with the single parameter d of templated type a <b , c>.
> Such was the wisdom of C++'s designers.
>
> When it is determined there is a pair of delimiters, they are marked as
> such with syntax-table text properties, but this marking is always done
> on both delimiters at once.
>
> In short, there is little chance of ever being able to insert angle
> brackets as a pair in C++ Mode.  Sorry!
>
>> The documentation for the variable sekeleton-pair-alist says,
>
>> [...]
>> Each alist element, which looks like (ELEMENT ...), is passed to
>> `skeleton-insert' with no interactor. Variable `str' does nothing.
>
>> Elements might be (?` ?` _ "''"), (?\( ? _ ")") or(?{ \n > _ \n ?} >).
>> [...]
>
>> I am sorry to say, I cant make a head or tail of this cryptic value
>> suggested for the variable.
>
> Sorry to say this, but neither can I.  I don't know what an "interactor"
> is, variable `str' is obscure, and it is totally unclear what the various
> example elements might mean.
>
>> Help solicited.
>
> Can I suggest you submit a bug report for this dreadful doc string?
>
>> Thanks,
>> r
>> -- 
>> (B.V. Raghav)

-- 
(B.V. Raghav)



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