[basics] Introduce concepts for referencing methods in documentation

[kjcole]

Bug Report

The tutorial on strings at https://crystal-lang.org/reference/1.2/tutorials/basics/40_strings.html reads:

To determine if a string is empty, you can check if the size is zero, or just use the shorthand String#empty?:

and later

The method String#blank? returns true if the string is empty or if it only contains whitespace characters. A related method is String#presence which returns nil if the string is blank, otherwise the string itself.

The # should be replaced with a . in each case.

[kjcole]

Actually, as I read further, I see consistent use of the # in the descriptions, and . in the interactive code examples... So, perhaps an explanation of why the text says "use ...#..." and then doesn't use "...#..." in the code examples.

(It's a beginners / basic tutorial, and stuff like that is confusing to beginners.)

[HertzDevil]

String.empty? refers to a class method. The # is correct when used to refer to an instance method. This convention comes from Ruby; our docs should indeed be friendlier towards readers with no Ruby experience (crystal-lang/crystal#8377). The problem is, at this point the tutorial doesn't even introduce OOP concepts yet, so there isn't anything we can do here for now.

Also issues related to the reference / tutorial should go to crystal-lang/crystal-book.