Questions tagged [instance-eval]
38 questions
23
votes
4 answers
Accessing Ruby Class Variables with class_eval and instance_eval
I have the following:
class Test
@@a = 10
def show_a()
puts "a: #{@@a}"
end
class << self
@@b = '40'
def show_b
puts "b: #{@@b}"
end
end
end
Why does following work:
Test.instance_eval{show_b}
b:…
haroldcampbell
- 1,512
- 1
- 14
- 22
9
votes
2 answers
Ruby difference between send and instance_eval?
I know send takes string or symbol with arguments while instance_eval takes string or block, and their difference could be apparent given receivers.
My question is what the 'under the hood' difference is for the example below?
1234.send 'to_s' …
Skiptomylu
- 964
- 1
- 13
- 21
8
votes
2 answers
class_eval vs instance_eval
Is there any difference in how class_eval & instance_eval work except def? Inside class_eval block def defines method to class itself (i.e. instance method) and inside instance_eval def defines method to the eigenclass of the class (i.e. class…
Alexey
- 9,197
- 5
- 64
- 76
7
votes
4 answers
Ruby instance_eval on a class with attr_accessor
I understand the basic difference between instance_eval and class_eval. What I've discovered though when playing around is something strange involving attr_accessor. Here's an example:
A = Class.new
A.class_eval{ attr_accessor :x }
a = A.new
a.x =…
brad
- 31,987
- 28
- 102
- 155
6
votes
1 answer
Ruby - Possible to pass a block as a param as an actual block to another function?
This is what I'm trying to do:
def call_block(in_class = "String", &block)
instance = eval("#{in_class}.new")
puts "instance class: #{instance.class}"
instance.instance_eval{ block.call }
end
# --- TEST EXAMPLE ---
# This outputs…
Markus O'Reilly
- 811
- 3
- 9
- 15
5
votes
1 answer
Where is instance_eval defined in Ruby 1.9.2?
Forgive my ignorance, but I must be missing something here. I can find the documentation for instance_eval for ruby 1.8.7 in the Object class, but I just cannot find it anywhere for 1.9.2. I know the functionality is still supported since I'm using…
elmt
- 1,604
- 14
- 24
5
votes
2 answers
Monkey patching built-in ruby classes in limited scopes
I'm working on an internal Ruby DSL and to make it look as pretty as possible I need to monkey patch the Symbol class and add some operators. I want to be responsible in how I do this and would like to limit the scope and lifetime of the patches to…
David K.
- 6,153
- 10
- 47
- 78
4
votes
3 answers
Ruby refinements with instance_eval
I'd like to provide some refinements to a DSL. I'm able to get refinements working with this example:
module ArrayExtras
refine Array do
def speak
puts 'array!'
end
end
end
module MyUniverse
using ArrayExtras
class Thing
…
Andy
- 285
- 3
- 12
4
votes
1 answer
Ruby Block Scope with instance_eval
My understanding of Ruby blocks and procs was that they are all closures. Now that I've seen it in use with instance_eval, I'm a little confused. What is the magic-sauce, the under workings when looking at the bare metal, that changes how a block's…
Chad M
- 943
- 1
- 9
- 22
3
votes
2 answers
Ruby: how does constant-lookup work in instance_eval/class_eval?
I'm working my way through Pickaxe 1.9, and I'm a bit confused by constant-lookup in instance/class_eval blocks. I'm using 1.9.2.
It seems that Ruby handles constant-lookup in *_eval blocks the same way it does method-lookup:
look for a definition…
Alan O'Donnell
- 1,276
- 9
- 17
3
votes
2 answers
ruby access instance variable in instance_eval
I am trying some ruby metaprogramming and got some confusion with instance_eval().
see below examples
@instance_var = 'instance_var'
local_var = 'local_var'
obj = Object.new
obj.instance_eval { p @instance_var; p local_var }
obj.instance_eval {…
Arthur H
- 43
- 5
3
votes
5 answers
Instance_eval does not work with do/end block, only with {}-blocks
If I have a class:
class KlassWithSecret
def initialize
@secret = 99
end
end
and run:
puts KlassWithSecret.new.instance_eval { @secret }
it prints 99, but if I run:
puts KlassWithSecret.new.instance_eval do
@secret
end
It returns an…
Alexander Popov
- 23,073
- 19
- 91
- 130
3
votes
1 answer
How does module_eval / class_eval / instance_eval counts the line numbers
I have found the line_number passed to class_eval, module_eval and instance_eval doesn't match the line numbers reported by the error. This behaviour is not explained by the ruby-doc which says: (use instance_eval as an example)
the optional…
steveyang
- 9,178
- 8
- 54
- 80
2
votes
1 answer
Dynamically added accessor assignment doesn't work when invoking block via instance_eval in Ruby
I have a class to which I add attribute accessors dynamically at runtime. This class forms part a DSL, whereby blocks get passed to configuration methods and invoked using instance_eval. This makes it possible in the DSL to remove references to…
VirtualStaticVoid
- 1,656
- 3
- 15
- 21
2
votes
1 answer
Deep into Ruby class_eval and instance_eval
class_eval and instance_eval are quite predictable in such cases like defining methods. I also understand the difference between class's instance and class's singleton (aka eigenclass).
BUT
I cannot figure out the only thing like following:
Let's…
bernstein7
- 111
- 5