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Records and Attributes

Scalars and arrays of the standard data types are not the only variables allowed by glish. Heterogeneous data structures, called records, can be treated as a single variable. These can be passed as arguments to a function and returned as a unit in a function return value. A record may be created all at once or added to piece by piece.

- header := [name='3C273', ra=12.12345, dec=2.3318]
- header.flux := 27.6
- header.type := 'quasar'
- print header.ra
12.12345

Record members may be strings, any of the numeric data types including arrays, as well as other records.

Any glish variable may be assigned attributes. For example,

- velocity::definition := 'relativistic'
- header.flux::units := 'Jy'

The distinction between record members and variable attributes is a subtle one, and it is seldom clear which is best suited to a particular application. Both record members and attributes may be accessed by name or by number. All of the following are acceptable:

- header.ra
- header[2]
- header['type']
- velocity::[1]
- velocity::definition
- velocity::['definition']

Numeric access lends itself to stepping through the fields or attributes with a loop index. Record field names may be retrieved with the built-in function 'field_names()', which returns a string.

- field_names(header)
name ra dec flux type

The empty attribute construct returns the attributes of a variable as a record, so you can use the 'field_names()' function on attributes, too.

- velocity::
[definition=relativistic]
- field_names(velocity::)
definition