From type/IO/Path

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method w(IO::Path:D: --> Bool:D)

Returns True if the invocant is a path that exists and is writable. The method will fail with X::IO::DoesNotExist if the path points to a non-existent filesystem entity.

From type/Proc/Async

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method w(Proc::Async:D:)

Returns a true value if :w was passed to the constructor, that is, if the external program is started with its input stream made available to output to the program through the .print, .say and .write methods.

From type/IO/Special

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method w(IO::Special:D: --> Bool)

The 'write access' file test operator, returns True only if this instance represents either the standard output (<STOUT>) or the standard error (<STDERR>) handle.