Note Ruby symbol hash shorthand notation isn't supported about crystal-book

[Blacksmoke16]

Yes, as @devnote-dev pointed out, there is no "shorthand notation". Using a : denotes a named tuple while => denotes a hash. This is somewhat pointed out in the hash docs:

https://crystal-lang.org/reference/1.7/syntax_and_semantics/literals/hash.html

Hashes are typically created with a hash literal denoted by curly braces ({ }) enclosing a list of pairs using => as delimiter between key and value and separated by commas ,.

NamedTuple literal docs don't directly point out that you use :, but its part of the example.

I'm hesitant to think we need to document these "warnings" explicitly in the literal docs for each type. Having something more descriptive for named tuples like we have for hashes would probably be sufficient. Adding an explicit section in the Crystal for Rubyists would be a better alternative as this page fits this topic more.

Going to transfer this issue to the crystal-book repo.

[devnote-dev]

The issue is that initializing a hash with symbol keys and constant values it is then instantiated as a NamedTuple instead of a Hash.
[...]

I tried the following code, it works as intended:

thing = {
  :foo => "foo",
  :bar => "bar"
}
puts typeof(thing) # => Hash(Symbol, String)

thing[:baz] = "baz"
puts thing # => {:foo => "foo", :bar => "bar", :baz => "baz"}

Also note that the syntax in your example is named tuple syntax, not hash syntax which uses =>.

Here are test cases, however, I have no idea in mind for unpredictable type at compile type to test if the a: b syntax will lead to Hash or NamedTuple in such a case.

Example A and B are hashes because you're using =>, their types are still known at compile time but it is not as strict as a named tuple, which C and D are because of :.

Having warnings in the documentation would be useful though, it's not exactly obvious that hashes use a specific syntax which can be confusing if you're coming from Ruby (or JavaScript, Python, etc).