Re: Accessing an element in an associativity list

[Tassilo Horn <tassilo@member.fsf.org>]

Joost Kremers <joostkremers@yahoo.com> writes:

Hi!

> (defvar c++-stl-containers
>   '(("string" "<string>" "String of char.")
>     ("wstring" "<wstring>" "String of wide char (wchar_t).")
>     ("vector" "<vector>" "Vectors contain contiguous elements stored as an array.")))
>
>> and I want to do something like this:
>>   (index-first 'c++-stl-containers "string" 2)
>> should evaluate to
>>   "<string>"
>> 
>> Is there any emacs lisp convenience function for accessing a row
>> given its, say, first (key) element?
>
> you can use ASSOC:
>
> (assoc "string" c++-stl-containers)
>
>   ===> ("string" "<string>" "String of char.")

For the sake of completeness:  To get to "<string>" from the key
"string" you'd use

      (cadr (assoc "string" c++-stl-containers))

here, which is a shortcut for

      (car (cdr (assoc "string" c++-stl-containers))).

Or you could use one of

      (nth 1 (assoc "string" c++-stl-containers))
      (second (assoc "string" c++-stl-containers)).

Bye,
Tassilo