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reflectioncrystal-lang

Compile time reflection over type members

I'd like to write a macro which will let me perform some operations on each attribute of a record, like deserialize a CSV row into the record instance with proper type casting. Where do I start from?

Solution

  • This is a very broad question. So I'll answer two different ones.

    How can I avoid code duplication using macros?

    Simple, just use a loop!

    numbers = [5, 3, 2, 1]

{% for operator in [:*, :+, :/, :-] %}
  numbers.map! {|number| number {{operator.id}} 23 }
{% end %}

p numbers

    [-17, -19, -20, -21]

    How can I get a list of all instance variables of a type at compile time?

    Via TypeNode#instance_vars!

    struct Bag 
  property has_wallet : Bool = false
  property has_bottle : Bool = false
  property has_keys : Bool = false
end

def fill_bag(bag)
  {% for name in Bag.instance_vars %}
  bag.{{name.id}} = true
  {% end %}
  bag
end

p fill_bag(Bag.new)

    Bag(@has_wallet=true, @has_bottle=true, @has_keys=true)