No way to use alias of NamedTuple in macros

[relonger]

crystal -v
Crystal 0.21.1 (2017-03-14) LLVM 4.0.0

alias TT = {a: Int32, b: String}

{% for k in TT.keys %}
  puts "{{k.name}}"
{% end %}

Generate errors:

undefined method 'keys' for TypeNode of type TT (must be a named tuple type)

{% for k in TT.keys %}
               ^~~~

But TT is exactly the NamedTuple (the alias of it). Tried a lot of combinations but nothing works - I can't access info about NamedTuple type after its declaration.

[asterite]

TT is an alias type, not a NamedTuple type.

The question is whether we want to remove the alias automatically here, or with an explicit operation.

[bew]

alias TT = {a: Int32, b: Char}
{% puts TT.class_name %}

Says it's a TypeNode, maybe we could add a macro method to TypeNode like TypeNode#alias? that would return the alias'd TypeNode if it's an alias type, and nil otherwise, so we could do something like:

alias TT = {a: Int32, b: Char}
{% puts TT.alias?.keys %} # => a, b

[relonger]

The question is whether we want to remove the alias automatically here, or with an explicit operation.

Either methods are suitable, but neither work now. There is now Alias type in Macro module.

[bew]

The question is whether we want to remove the alias automatically here, or with an explicit operation.

I'd say remove the alias automatically so TypeNode manipulations is transparent, but allow to check if it's an alias with .alias?:

alias TT = {a: Int32, b: Char}

# type manipulation
{% puts TT.class_name %} # => NamedTuple
{% puts TT.keys %} # => [a, b]

# alias?
{% puts TT.alias? %} # => AliasType (or something similar)
{% puts TT.alias?.name %} # => TT

[veelenga]

Another case is union types:

alias TT = Int32 | String

{% puts TT.union? %} #=> false
{% puts TT.union_types %}  #=> undefined method 'union_types' for TypeNode of type TT (must be a union type)

[ozra]

I'm in favour of explicit operation; TT is an Alias-node. It shouldn't disappear in thin air!? Just a method to get the "target-node"/"aliased node" from the alias-node and then get down to business.