I can't figure out the proper block initialize
class Foo
attr_accessor :bar
end
obj = Foo.new do |a|
a.bar = "baz"
end
puts obj.bar
Expect "baz" instead get nil
What is the proper incantation for block class initializers in ruby?
4 Answers
Another way to make a block initializer would be writing it yourself one:
class Foo
attr_accessor :bar
def initialize
yield self if block_given?
end
end
And later use it:
foo = Foo.new do |f|
f.bar = true
end
My two cents.
1 Comment
Rodrigo Dias
no doubt this is the better way of initializing a class with a block.
Try again:
class Foo
attr_accessor :bar
end
obj = Foo.new.tap do |a|
a.bar = "baz"
end
puts obj.bar
3 Comments
Niklas B.
That's not the same. Also, it should raise a
NameError.
Reactormonk
It's the best way without adding new ways your users have to read the documentation for.
Jon Snow
This way is better than putting
yield self if block_given? in the Foo's initialize method, because often you can't or don't want to modify the Foo class (think of the Open Closed Principle). Plus, why clutter up the initialize method of the Foo class, when a simple method chaining of tap would do?I don't think Never saw it anywhere anyway. Why do you want to initialize in a block ? You can always do new can take a block.obj = foo.new.tap do |a| ... If you really want a block
4 Comments
Niklas B.
It's not that it can't take a block, it's just ugly. Despite this, it's a commonly seen "idiom".
Doug
Why is it ugly? It's a common idiom in other languages that I've used such as c#.
Niklas B.
@Doug: It's equally ugly in other languages, the main reason for it being that it doesn't serve any particular purpose and just increases complexity.
Doug
It seems clearer and less error-prone to me. There's no order dependency as in a normal constructor, and you get named parameters which are easier to read and write. I'd probably only resort to a constructor if there was some initialization beyond copying in values (which is not always the case)
actually you have a constructor for these purposes:
class Foo
attr_accessor :bar
def initialize(bar = "baz")
@bar = bar
end
end
attr_accessorcan't work in that form and the block is never called.FactoryGirlwhere this would be of advantage?