misc #8905

Add documentation to semantics of method default arguments

Added by Ilya Vorontsov 7 months ago. Updated 7 months ago.

[ruby-core:57175]
Status:Open
Priority:Normal
Assignee:Zachary Scott
Category:doc
Target version:-

Description

In http://www.ruby-doc.org/core-2.0.0/doc/syntax/methods_rdoc.html one can see simple uses of default parameters. But I couldn't find any rules on default parameters, which are calculated in a runtime such as context and order of assignments. And whether this order is always well defined? Usually it's left to right, are there any exceptions for keyword arguments or splats?

I've made a bit of tests to make am intuition of using default arguments but missed lots of corner cases. Which probably should be documented, but simple cases should be documented too.

class A
def f
'A#f'
end
def self.f
'A.f'
end
def g(arg = f)
puts arg;
end
def self.g(arg = f)
puts arg
end
def h(arg1 = f, arg2 = '(' +arg1 + ')')
puts "#{arg1}, #{arg2}"
end
def j(arg1 = 2*arg2, arg2 = f)
puts "#{arg1}, #{arg2}"
end
end

A.g # => 'A.f'
instance = A.new
instance.g # => 'A#f'
instance.h # => 'A#f, (A#f)'
instance.j # => Undefined local variable or method arg2 for #

History

#1 Updated by Nobuyoshi Nakada 7 months ago

It's defined as left-to-right order, always.

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