Constrained genericity: Difference between revisions

=={{header|Crystal}}==

Similar to Ruby version, but shows error at compile-time.

<lang ruby>class Apple

def eat

end

end

class Carrot

def eat

end

end

class FoodBox(T)

def initialize(@data : Array(T))

{% if T.union? %}

{% raise "All items should be eatable" unless T.union_types.all? &.has_method?(:eat) %}

{% else %}

{% raise "Items should be eatable" unless T.has_method?(:eat) %}

{% end %}

end

end

FoodBox.new([Apple.new, Apple.new])

FoodBox.new([Apple.new, Carrot.new])

FoodBox.new([Apple.new, Carrot.new, 123])</lang>

{{out}}

<pre>

Error in line 23: All items should be eatable

</pre>