On Sun, May 31, 2020 at 04:06:28PM -0700, ToddAndMargo via perl6-users wrote:
On 2020-05-31 12:48, Veesh Goldman wrote:
well, literally it would mean something like "a direct result of
inability to read is to not understand", which in context should mean if
you can't read you won't understand. But I think the point was made.
Hi Veesh,
Please help me with my reading skills here.
https://docs.raku.org/routine/starts-with
multi method starts-with(Str:D: Str(Cool) $needle, :i(:$ignorecase),
:m(:$ignoremark) --> Bool:D)
Does this or does this not state that the "Haystack"
(invocant) is required to be defined ("Str:D:")?
Yes, it does. Good!
If I am reading it correctly, is requires a "defined"
("D") Haystack (invocant). Am I misreading something?
No, you're not - or at least, only slightly, see below.
Running a test, the method DO NOT check for defined:
p6 'my $x; say $x.starts-with( "1" );'
No such method 'starts-with' for invocant of type
'Any' in block <unit> at -e line 1
What am I misreading? Does it say anywhere that the
Haystack in not defined? Does it way anywhere that I
violated the requirement that the Haystack be defined?
And what is "No such method 'starts-with'" suppose to
mean? I am staring at the method on right on the manual
page. Did the developers forget to include "opens-with"
on my version of Raku? Obvious it does not mean what
it says. Unless my reading skill really suck.
Try it with something slightly different, give Raku something to
work with :)
[roam@straylight ~]$ raku -e 'my Str $x; $x.starts-with("1")'
Cannot resolve caller starts-with(Str:U: Str:D); none of these signatures match:
(Cool:D: Cool:D $needle, :i(:$ignorecase)!, :m(:$ignoremark), *%_ --> Bool)
(Cool:D: Cool:D $needle, :m(:$ignoremark)!, *%_ --> Bool)
(Cool:D: Cool:D $needle, *%_ --> Bool)
(Str:D: Str:D $needle, :i(:$ignorecase)!, :m(:$ignoremark), *%_ --> Bool)
(Str:D: Str:D $needle, :m(:$ignoremark)!, *%_ --> Bool)
(Str:D: Str:D $needle, *%_ --> Bool)
in block <unit> at -e line 1
[roam@straylight ~]$
The difference is that you said "my $x", thus making $x an undefined
variable of the "Any" type (since you did not specify a type), and
I said "my Str $x", thus making $x an undefined string. Once Raku knows
that $x is supposed to be a string, it can look for a .starts-with()
method in the Str class and in all its parent classes - and it finds
some methods in Str and some methods in the class named Cool.
Also, lets add to my reading comprehension, the Needle:
`Str(Cool) $needle`
I do not see "D" or "U" anywhere. Am I missing something?
A test:
$ p6 'my $x; say "abc".starts-with( $x );'
Cannot resolve caller starts-with(Str:D: Any:U);
none of these signatures match: ...
Hm, this one is interesting. On the one hand, your test was once again
slightly wrong, once again you should have declared $x to be a Str.
On the other hand, even with the corrected test:
[roam@straylight ~]$ raku -e 'my Str $x; dd "abc".starts-with($x);'
Cannot resolve caller starts-with(Str:D: Str:U); none of these signatures match:
(Cool:D: Cool:D $needle, :i(:$ignorecase)!, :m(:$ignoremark), *%_ --> Bool)
(Cool:D: Cool:D $needle, :m(:$ignoremark)!, *%_ --> Bool)
(Cool:D: Cool:D $needle, *%_ --> Bool)
(Str:D: Str:D $needle, :i(:$ignorecase)!, :m(:$ignoremark), *%_ --> Bool)
(Str:D: Str:D $needle, :m(:$ignoremark)!, *%_ --> Bool)
(Str:D: Str:D $needle, *%_ --> Bool)
in block <unit> at -e line 1
[roam@straylight ~]$
And here we come to the interesting part: it seems that the
documentation is wrong here, since what Raku says is that the
.starts-with() method of the Str class really wants a `Str:D $needle` -
it does expect its argument to be defined.
Okay, now it tells me "Any:U" for the needle. It
is telling me that I sent it a undefined value. To
me, that is a good troubleshooting hint. Am I
misreading it?
Well, it's actually telling you that you *passed* an Any:U object :)
Yes, it's telling you that it cannot find a method .starts-with() that
will accept an undefined object of the "Any" type as a parameter,
so, yeah, getting close :)
Now what I would "like to see" (suggestion, not a demand),
is the Haystack complain in a similar fashion. For instance:
starts-with's invocant requires a defined value (Str:D)
Have I misread anything?
See above - you'll get this if you declare $x as a Str :)
But, yes, you're making progress, great!
G'luck,
Peter
