obj.extend(Methods) should update type definition obj with the methods of Methods

[HoneyryderChuck]

this type of extension of type definitions isn't being done by steep on type analysis via steep check.

# given
class A
  def foo: () -> void
end

module B
  def bar: () -> void
end

# following code should be correctly checked
a = A.new
a.extend(B)
a.bar

[soutaro]

Same for #1064. You can annotate the type of the object using intersection type.

a = A.new
b = a.extend(B) #: A & B

[HoneyryderChuck]

@soutaro steep does not support syntax to switch a variable's type mid-code. A similar but perhaps clearer example of what happens is:

# given type a: Array[Number | :stop]
a = [1, 2, :stop]

a.delete(:stop)

# and given def func: (Array[Number]) -> void
func(a)

steep will signal a type error on that last call, given that a is still an "array of numbers of stop" at that point, despite the operation above. adding an annotation beforehand like @type var a: Array[Number] won't help, as steep will apply that signature to a.delete(:stop), which will error from then on, despite it being placed before the annotation.

[soutaro]

The scope of type annotations is not very clear and might be confusing... Generally, it's based on the scope of local variables in Ruby. a is the same variable through the lines, so the @type annotation applies to all of the occurrence of a.

For this specific example, assigning to a itself with type assertion works.

a = [1, 2, :stop]

a.delete(:stop)

a = a #: Array[Integer]

# a is Array[Integer] here

(💡 It works even without delete call...)