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-rw-r--r--lib/asn1/doc/src/asn1_ug.xml66
1 files changed, 4 insertions, 62 deletions
diff --git a/lib/asn1/doc/src/asn1_ug.xml b/lib/asn1/doc/src/asn1_ug.xml
index a16aac0e03..dd08eb1817 100644
--- a/lib/asn1/doc/src/asn1_ug.xml
+++ b/lib/asn1/doc/src/asn1_ug.xml
@@ -949,68 +949,10 @@ ok
<section>
<marker id="SET"></marker>
<title>SET</title>
- <p>The SET type is an unusual construct and normally the SEQUENCE
- type is more appropriate to use. Set is also inefficient compared with SEQUENCE, as the components can be in any order. Hence, it must be possible
- to distinguish every component in 'SET', both when
- encoding and decoding a value of a type defined to be a SET.
- The tags of all components must be different from each other
- in order to be easily recognizable.</p>
- <p>A SET may be defined as:</p>
- <pre>
-Pdu2 ::= SET {
- a INTEGER,
- b BOOLEAN,
- c ENUMERATED {on(0),off(1)} } </pre>
- <p>A SET is represented as an Erlang record.
- For each SEQUENCE and <c>SET</c> in
- an ASN.1 module an Erlang record declaration is generated. For
- <c>Pdu2</c> above a record is defined like this:</p>
- <pre>
--record('Pdu2',{a, b, c}). </pre>
- <p>The record declarations for a module <c>M</c> are placed in a
- separate <c>M.hrl</c> file.</p>
- <p>Values can be assigned in Erlang as demonstrated below:</p>
- <pre>
-V = #'Pdu2'{a=44,b=false,c=off}. </pre>
- <p>The decode functions will return a record as result when decoding
- a SET.
- </p>
- <p>The difference between SET and SEQUENCE is that the order of
- the components (in the BER encoded format) is undefined for SET
- and defined as the lexical order from the ASN.1 definition for
- SEQUENCE. The ASN.1 compiler for Erlang will always encode a
- SET in the lexical order. The decode routines can handle SET
- components encoded in any order but will always return the
- result as a record. Since all components of the SET must be
- distinguishable both in the encoding phase as well as the
- decoding phase the following type is not allowed in a module
- with EXPLICIT or IMPLICIT as tag-default :</p>
- <p></p>
- <pre>
-Bad ::= SET {i INTEGER,
- j INTEGER } </pre>
- <p>The ASN.1 to Erlang compiler rejects the above type. We
- shall not explain the concept of tag further here, we refer to
- [<cite id="X.680"></cite>].
- </p>
- <p>Encoding of a SET with components with DEFAULT values behaves
- similar as a SEQUENCE. The DER encoding format restrictions on DEFAULT
- values is the same for SET as for SEQUENCE, and is supported by
- the compiler.</p>
- <p>Moreover, in DER the elements of a SET will be sorted. If a
- component is an un-tagged choice the sorting have to take place
- in run-time. This fact emphasizes the following recommendation
- if DER encoding format is used.</p>
- <p>The concept of SET is an unusual
- construct and one cannot think of one single application
- where the set type is essential. (Imagine if someone
- "invented'' the shuffled array in 'C') People tend to think
- that 'SET' sounds nicer and more mathematical than 'SEQUENCE'
- and hence use it when 'SEQUENCE' would have been more
- appropriate. It is also most inefficient, since every correct
- implementation of SET must always be prepared to accept the
- components in any order. So, if possible use SEQUENCE instead
- of SET.</p>
+ <p>In Erlang, the SET type is used exactly as SEQUENCE. Note
+ that if the BER or DER encoding rules are used, decoding a
+ SET is slower than decoding a SEQUENCE because the components
+ must be sorted.</p>
</section>
<section>