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what type $in,$out and $err is

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From:
Xiao Yafeng
Date:
October 28, 2018 19:24
Subject:
what type $in,$out and $err is
Message ID:
CABPUXgC-S0eyqx2T05zngAOuyj215XSNBqrabwfWyR-t2m-Vxg@mail.gmail.com
I'm curious about what type of $in is on Proc class. As described in perl6doc:
$in, $out and $err are the three standard streams of the
to-be-launched program, and default to "-" meaning they inherit the
stream from the parent process. Setting one (or more) of them to True
makes the stream available as an IO::Pipe object of the same name,
like for example $proc.out.

I mean, if $in is IO::Pipe object, how can I pass it True?

> my IO::Pipe $bb = True;
Type check failed in assignment to $bb; expected IO::Pipe but got Bool
(Bool::True)
  in block <unit> at <unknown file> line 4

I'm interested in the underlying mechanics of  it. Please enlighten me.

Besides, just curious, why choose '_' as default it looks strange....

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