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| operator | referents is attached | ||||||||
Return type: Boolean Returns true when the contents are defined or have been defined, and false otherwise. Replacing
Returns: is with isnt will reverse the results
Syntax
this? referents indexer? (is | isnt) attached
A referent is attached when its contents have been defined. However, the referent is no longer attached if a particular referent's contents have been specified, the referent has been closed, and the stream bound to that referent is subsequently discarded.
this indicates the currently selected referent. Indexer is a phrase identifying which referent is to be examined. The two cannot be combined.
This code sample illustrates using the "referents...is attached" test. The sample also shows that if a referent has been closed and the stream bound to that referent discarded, then the referent is no longer attached.
macro attach-check token ref-name is
do when referents{ref-name} is attached
output "attached%n"
else
output "not attached%n"
done
macro-end
process
local stream s
output referent "x" ; referent "x" is not attached
attach-check "x"
open s as referent "x" ; referent "x" is attached now
attach-check "x"
put s "some contents%n" ; still attached
attach-check "x"
close s ; still attached
attach-check "x"
discard s ; referent "x" is no longer attached
attach-check "x"
set referent "x" to "more contents%n"
attach-check "x" ; attached now so we end up with a value
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Related Syntax referents |
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