27 Records

Records are next to lists the most important way to collect objects together. A record is a collection of components. Each component has a unique name, which is an identifier that distinguishes this component, and a value, which is an object of arbitrary type. We often abbreviate value of a component to element. We also say that a record contains its elements. You can access and change the elements of a record using its name.

Record literals are written by writing down the components in order between ``rec('' and ``)'', and separating them by commas ``,''. Each component consists of the name, the assignment operator :=, and the value. The empty record, i.e., the record with no components, is written as rec().

gap> rec( a := 1, b := "2" ); # a record with two components
rec(
 a := 1,
 b := "2" )
gap> rec( a := 1, b := rec( c := 2 ) ); # record may contain records
rec(
 a := 1,
 b := rec(
       c := 2 ) )

Records usually contain elements of various types, i.e., they are usually not homogeneous like lists.

IsRecord( obj ) C

IsRecordCollection( obj ) C

IsRecordCollColl( obj ) C

gap> IsRecord( rec( a := 1, b := 2 ) );
true
gap> IsRecord( IsRecord );
false

RecNames( rec ) A

returns a list of strings corresponding to the names of the record components of the record rec.

gap> r := rec( a := 1, b := 2 );;
gap> RecNames( r );
[ "a", "b" ]

Note that you cannot use the string result in the ordinary way to access or change a record component. You must use the rec.(name) construct (see Accessing Record Elements and Record Assignment).

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GAP 4 manual
February 2000