zap()
creates a sentinel object that indicates that an object
should be removed. For instance, named zaps instruct env_bind()
and call_modify()
to remove those objects from the environment or
the call.
The advantage of zap objects is that they unambiguously signal the
intent of removing an object. Sentinels like NULL
or
missing_arg()
are ambiguous because they represent valid R
objects.
zap() is_zap(x)
x | An object to test. |
---|
# Create one zap object: zap() #> <zap> # Create a list of zaps: rep(list(zap()), 3) #> [[1]] #> <zap> #> #> [[2]] #> <zap> #> #> [[3]] #> <zap> #> rep_named(c("foo", "bar"), list(zap())) #> $foo #> <zap> #> #> $bar #> <zap> #>