[erlang-questions] Erlang basic doubts about String, message passing and context switching overhead

Jesper Louis Andersen jesper.louis.andersen@REDACTED
Fri Jan 13 13:20:05 CET 2017

Richard is indeed right, depending on what your definition of "String" is.

If a "String" is "An array of characters from some alphabet", then you need
to take into account Strings are Unicode codepoints in practice. This is
also the most precise definition from a technical point of view.

When I wrote my post, I was--probably incorrectly--assuming the older
notion of a "String" where the representation is either ASCII or something
like ISO-8859-15. In this case, a string coincides with a stream of bytes.

Data needs parsing. A lot of data comes in as some kind of stringy
representation: UTF-8, byte array (binary), and so on.

And of course, that isn't the whole story, since there are examples of
input which are not string-like in their forms.

On Fri, Jan 13, 2017 at 2:34 AM Richard A. O'Keefe <ok@REDACTED>

> On 13/01/17 8:56 AM, Jesper Louis Andersen wrote:
> > Strings are really just streams of bytes.
> That was true a long time ago.  Maybe.
> But it isn't anywhere near accurate as a description
> of Unicode:
>   - Unicode is made of 21-bit code points, not bytes.
>   - Most possible code points are not defined.
>   - Some of those that are defined are defined as
>     "it is illegal to use this".
>   - Unicode sequences have *structure*; it is simply
>     not the case that every sequence of allowable
>     Unicode code points is a legal Unicode string.
>   - As a special case of that, if s is a non-empty
>     valid Unicode string, it is not true that every
>     substring of s is a valid Unicode string.
> In case you were thinking of UTF-8, not all byte
> sequences are valid UTF-8.
> Byte streams are as important as you say, but it's
> really hard to see the software for a radar or a
> radio telescope as processing strings...
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