[erlang-questions] Types and specs [WAS: [enhancement] string:split/2]

Kostis Sagonas <>
Fri Oct 10 13:33:12 CEST 2008


Richard O'Keefe wrote:
> 
> Can anyone explain to me why
> 
> -spec(tokens/2 :: (string(), string()) -> [[char(),...]]).
> 
> doesn't mention "string()" on the right hand side of the arrow?

There is no native string() type in Erlang, as we all well know.

So, in the language ot types, string() is just an alias for the type 
list(char()), which, for convenience, is typically written as [char()]. 
  This can include both the empty string "" == [] and a non-empty list 
of characters, which is denoted [char(),...].  That's what the above 
spec signifies: the resulting list consists of non-empty strings, which 
is consistent with what string:tokens/2 actually returns.  Hope this 
explains things.

On the other hand, I can see how this may look a bit strange to some and 
have for a long time now pondered whether a non_empty_string() type 
alias might be added to the list of built-in types.

Kostis



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