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Re: internal data structure

From: Emanuel Berg
Subject: Re: internal data structure
Date: Sat, 20 May 2017 16:33:02 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux)

Alexander Doe wrote:

> which data structure is used by GNU/Emacs for
> storing and editing text strings on
> low-level? List, balanced tree, gap buffer,
> something else?
> Which language is used for programming this?
> C or ELisp?

Emacs is Lisp on top of C.

The strings in Lisp are data objects that are
string-typed. This contrary to a language like
C where it is the *variable*, non the data
object, that is associated with a type.

That said, there isn't a string type in C.
In C what you do is either you have an array of
chars, or you have a pointer to a char and then
continue in memory a certain number of bytes,
which is the length of the text string, as
1 char is stored as 1 byte.

In practice, the array and pointer methods in
C amount to virtually the same.

By the way, "char" is pronounced "kar"!

In Lisp, or Elisp at least, because everything
is lists, it is tempting to think of a string
as a list of chars, just like the C array.
But technically, this is not the case:

    (stringp "Sail Ho!")              ; t
    (listp   "True sailing is dead.") ; nil

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