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substrraku

Perl6: why does substr-rw behave this way?

Why does here substr-rw cut off the trailing 6?

#!/usr/bin/env perl6
use v6;

my $str = '123';
$str ~= '.' x 30;
$str ~= '456';

say $str;       #   123..............................456
$str.substr-rw( 0, 10 ) = '';
say $str;       #   ........................45

perl6 --version
This is Rakudo version 2016.03-38-g8df1a69 built on MoarVM version 2016.03-46-g50c7f6a implementing Perl 6.c.
Solution

  • UPDATE: A Rakudo/MoarVM built after 2016-07-21 should behave correctly.

    Looks like a bug to me. Note that it matters how the string is constructed:

    my $a = '.' x 3 ~ 'x';
my $b = sprintf('%s', $a); # or just '...x', but not "$a"

say $a; #=> ..x
say $b; #=> ..x

$a.substr-rw( 0, 2 ) = '';
$b.substr-rw( 0, 2 ) = '';

say $a; #=> ..
say $b; #=> .x

    Update: The bug has been reported: RT#127782