The Pearls of Raku, Issue 3: tr, TR, and StrDistance
source link: https://andrewshitov.com/2020/07/25/the-pearls-of-raku-issue-3/
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Hello! Today, let me show three small but interesting things that you might skip when reading the documentation to the Raku programming language (if you did read it :-).
Table of Contents
tr
ad TR
There is a pair of transliteration (or transformation) operators in Raku: tr
and TR
. As you may guess from the name, they have something in common. But there are also some differences.
The lower case tr
performs an in-place substitution:
my $s = 'Hello, World!'; $s ~~ <strong>tr</strong>/o/ó/; say $s; # Helló, Wórld!
The target string is updated after the operation.
Unlike that, TR
does not change the string and returns the new string as a result.
my $s = 'Hello, World!'; my $r = <strong>TR</strong>/o/ó/ <strong>with</strong> $s; say $s; # Hello, World! say $r; # Helló, Wórld!
Note that you cannot simply write my $r = $s ~~ TR/o/ó/
, but instead you need to set the topic first, for example,using with
. You can do the same with the lowercase version, too:
tr/o/ó/, .say with $s; # Helló, Wórld!
StrDistance
OK, what happens if you save the result of matching with tr
as in the following snippet?
my $s = 'Hello, World!'; <strong>my $r = $s ~~ tr/o/ó/;</strong>
Unlike the probable expectation, you do not simply get the new string in $r
. The type of that object is StrDistance
.
say $r.WHAT; # (StrDistance)
When being coerced to a string, it gives you the string—the modified string after the replacement in our case. When it is coerced to an integer, you get the number of replacements happened:
say <strong>~</strong>$r; # Helló, Wórld! say <strong>+</strong>$r; # 2
The variable also keeps both original and modified versions of the string:
say $r.before; say $r.after;
put vs get
The third thing to cover in this post is to see the difference between put
and say
, when they are called with the StrDistance
object.
The difference between put
and say
is that put
internally calls .Str
on an object, while say
calls .gist
.
From the previous section, we know that if a StrDistance
is converted to a string, it gives a string, so in our example, you see the updated string after the transliteration:
<strong>put</strong> $r; # Helló, Wórld!
With say
, you see more details about the contents:
<strong>say</strong> $r; # StrDistance.new(before => "Hello, World!", after => "Helló, Wórld!")
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