If a method does not explicitly specify its invocant type, it is set
to the type of the enclosing class.
The `cos` method is declared in the `Cool` class, so that is its
invocant type.
The doc shows that it's declared in the `Cool` class.
So, the doc is fine as is for the invocant.
The returned value is a cosine, which, per the linked doc,
is a real number. The doc could perhaps show a return value
of Real:D.
On Mon, Dec 21, 2020 at 12:05 AM ToddAndMargo via perl6-users
<perl6-us...@perl.org> wrote:
>
> On 12/20/20 1:18 PM, Bruce Gray wrote:
> >
> >
> >> On Dec 20, 2020, at 2:54 AM, ToddAndMargo via perl6-users
> >> <perl6-us...@perl.org> wrote:
> >
> > —snip--
> >
> >> I obviously can't feed it a string.
> >
> > Obviously you cannot, but actually you can!
> >
> > $ raku -e 'say .cos for 42, "42", ("4" ~ "2"), "5421".substr(1,2);'
> > -0.3999853149883513
> > -0.3999853149883513
> > -0.3999853149883513
> > -0.3999853149883513
> >
> > The subroutine form in https://docs.raku.org/routine/cos is declared as:
> > sub cos(Numeric(Cool))
> > and the text specifies:
> > Coerces the invocant (or in sub form, the argument) to Numeric,
> > interprets it as radians, returns its cosine.
> > , so the string “42” is coerced to the number 42 as it is passed to cos().
> > This kind of coercion is not often needed in user code, but the code of the
> > Raku core needs to coerce to maintain a key element of Perl&Raku design:
> > * If the coder treats something as a number, then the language acts
> > on it as if it is a number, even if it has to convert a string to a number
> > behind the scenes at runtime.
> > * If the coder treats something as a string, then the language acts
> > on it as if it is a string, even if it has to convert a number to a string
> > behind the scenes at runtime.
> > (BTW, both Perl and Raku use an amazingly efficient auto-caching of this
> > string-vs-number duality; many newcomers think the conversion must be a
> > performance hog, but it is not.)
> >
> > For details on the syntax of automatic coercion during a subroutine call,
> > see:
> > https://docs.raku.org/type/Signature#Coercion_type
> > (Most users never need in their own code, but you saw it by reading the
> > Raku core, so please take that as just for your curiosity and not as a new
> > technique looking for a place in your own designs.)
> >
> >> On Dec 20, 2020, at 2:17 AM, ToddAndMargo via perl6-users
> >> <perl6-us...@perl.org> wrote:
> >> https://docs.raku.org/routine/cos
> >> method cos()
> >> Where is the definition of what is fed to the method?
> > —snip—
> > The definition is hiding right in front of us :^)
> > Just like (in another thread) you defined `method BadAdd () {…}`, the `cos`
> > method has open+close parens to show that it has empty Signature. It takes
> > no arguments, and will complain if you try to pass an argument to it.
> > All methods automatically have access to the invoking object, via “self”
> > (and other shortcuts like $.attribute_name).
> > When you call `42.cos`, `42` is the invoking object, and that one value is
> > all that .cos needs.
> >
> >
> >> On Dec 20, 2020, at 2:25 AM, ToddAndMargo via perl6-users
> >> <perl6-us...@perl.org> wrote:
> >
> > —snip--
> >
> >> https://github.com/rakudo/rakudo/blob/master/src/core.c/Cool.pm6
> >>
> >> 13: method cos() { self.Numeric.cos }
> >>
> >> Whatever the heck "self” is
> >
> > “self” is the “current” object instance (called the “invocant”).
> > https://docs.raku.org/language/terms#term_self
> > When you define a method in a Class, you are writing sort of abstractly,
> > because at any given time you might have many objects (called “instances”)
> > of that Class, all alive and working in your program at the same time.
> > In most languages that support OO, there is a magic keyword like “this” or
> > “self” that refers to *only* that single instance that called the method.
> > In Raku, “self” is that keyword, but you can override it to a variable name
> > of your choice , if that makes more sense in your code.
> > my Str $a = ’15';
> > my Str $b = '37';
> > say $b.cos;
> > Inside method `cos`, during the .cos call in the code above, “self” is an
> > alias to $b .
> >
> >
> > —
> > Hope this helps,
> > Bruce Gray (Util of PerlMonks)
> >
>
>
> Going back to the original question,
>
> should not the doc page say?
>
> method cos( Cool:D: --> Cool:D )
