How to define_method with a do and end - ruby

I am writing a program that utilizes define_method, but I don't understand how I could define a method like this one:
def mymethod(variable) do
puts variable
puts yield
end
Which can be called by:
mymethod("hi") do
# this is yield
end

You cannot use yield. You need to receive it as a proc object.
define_method(:mymethod) do |variable, &block|
puts variable
puts block.call
end
mymethod("foo"){"bar"}
# foo
# bar
mymethod("foo") do "bar" end
# foo
# bar

define_method :my_method do |str, &block|
# Do something here
yield # or block.call
# Do something here
end

Related

Weirdness with around aspect in ruby

I am new to ruby
Trying to write an around aspect. My code is as follows
My code looks as follows
module Utils
module Aspects
def self.included(base)
base.extend(self)
end
def around_aspect(method_name, before_proc, after_proc)
code = %Q[
def #{method_name} *args, &block
#{before_proc.call}
old_#{method_name} *args, &block
#{after_proc.call}
end
]
class_eval %Q[
alias_method :old_#{method_name}, :#{method_name}
]
class_eval code
end
# def before_aspect method_name, before_proc
# around_aspect method_name, before_proc, ->(){}
# end
#
# def after_aspect method_name, after_proc
# around_aspect method_name, ->(){}, after_proc
# end
end
end
class Test
include Utils::Aspects
def test
puts 'test'
end
before = ->(){puts 'before'}
after = ->(){puts 'after'}
around_aspect :test,before,after
end
Test.new.test
The problem is that when i do Test.new.test I expect it to print
before, test and after" in order. But right now it prints "before,after and test"
The problem is that when i do Test.new.test I expect it to print
before, test and after" in order. But right now it prints "before,after and test"
No, it doesn't. When calling Test.new.test it only prints test. before and after are printed when defining the wrapped method, i.e. when calling around_advice.
Try to put a puts in between the call to around_advice and the call to Test.new.test (and try to call test several times) to observe this:
puts '______________________'
Test.new.test
Test.new.test
# before
# after
# ______________________
# test
# test
You are calling the lambdas only once, when defining the method:
code = %Q[
def #{method_name} *args, &block
#{before_proc.call}
# ^^^^^^^^^^^^^^^^^^^
old_#{method_name} *args, &block
#{after_proc.call}
# ^^^^^^^^^^^^^^^^^^
end
]
You need to call them every time when calling the method:
code = %Q[
def #{method_name} *args, &block
before_proc.call
old_#{method_name} *args, &block
after_proc.call
end
]
However, it would be much easier to just use Module#prepend, after all, that's what it's there for:
module Aspects
refine Module do
def around_aspect(method_name, before_proc, after_proc)
prepend(Module.new do
define_method(method_name) do |*args, &block|
before_proc.()
super(*args, &block)
after_proc.()
end
end)
end
end
end
class Test
using Aspects
def test
puts 'test'
end
before = -> {puts 'before'}
after = -> {puts 'after'}
around_aspect :test, before, after
end
Just putting my code up here. This is how i ended up achieving what i was trying to do, module.prepend as suggested above is another way
module Utils
module Aspects
def self.included(base)
base.extend(self)
end
def around_aspect(method_name, before_proc, after_proc)
new_method_name = Random.new_seed.to_s
alias_method :"#{new_method_name}", :"#{method_name}"
define_method "#{method_name}" do |*args, &block|
before_proc.call
send(:"#{new_method_name}", *args, &block)
after_proc.call
end
end
def before_aspect method_name, before_proc
around_aspect method_name, before_proc, ->(){}
end
def after_aspect method_name, after_proc
around_aspect method_name, ->(){}, after_proc
end
end
end
class Test
include Utils::Aspects
def test
puts 'test'
end
before = ->(){puts 'before'}
after = ->(){puts 'after'}
before_aspect :test, before
after_aspect :test, after
end
Test.new.test

How do I pass a block with other arguments?

def test(args,&block)
yield
end
test 1, {puts "hello"}
Last line doesn't work. How do I pass a block with other arguments?
test(1){ puts "hello" }
or
test(1) do
puts "hello"
end
or
blk = proc{ puts "hello" }
test(1, &blk)
You can check out this https://pine.fm/LearnToProgram/chap_10.html
As #Cary Swoveland suggested we can go slightly deeper.
Any Ruby method can implicitly accept a block. And even though you didn't define it in your method signature you still can capture it and pass further.
So, considering this idea we can do following manipulations with your method:
def test(args, &block)
yield
end
is the same as
def test(args)
yield
end
and the same as
def test(args)
block = Proc.new
block.call
end
When you have this implicit block capturing you'd probably want to add extra check:
def test(args)
if block_given?
block = Proc.new
block.call
else
"no block"
end
end
or
def test(args)
if block_given?
yield
else
"no block"
end
end
So calling these methods will return following:
test("args")
#=> no block
test("args"){ "Hello World" }
#=> "Hello World"

Yielding a block to a proc (or creating a method that accepts a block from a proc that yields)

I'm currently working on an interface that allows me to wrap arbitrary method calls with a chain of procs. Without going into too much detail, I currently have an interface that accepts something like this:
class Spy
def initialize
#procs = []
end
def wrap(&block)
#procs << block
end
def execute
original_proc = Proc.new { call_original }
#procs.reduce(original_proc) do |memo, p|
Proc.new { p.call &memo }
end.call
end
def call_original
puts 'in the middle'
end
end
spy = Spy.new
spy.wrap do |&block|
puts 'hello'
block.call
end
spy.wrap do |&block|
block.call
puts 'goodbye'
end
spy.execute
What I'd like to do though is remove the |&block| and block.call from my API and use yield instead.
spy.wrap do
puts 'hello'
yield
end
This didn't work and raised a LocalJumpError: no block given (yield) error.
I've also tried creating methods by passing the proc the define_singleton_method in the reduce, but I haven't had any luck.
def execute
original_proc = Proc.new { call_original }
#procs.reduce(original_proc) do |memo, p|
define_singleton_method :hello, &p
Proc.new { singleton_method(:hello).call(&memo) }
end.call
end
Is there another approach I can use? Is there anyway to yield from a Proc or use the Proc to initialize something that can be yielded to?
Using yield in your wrap block does not make much sense unless you passed a block to the caller itself:
def foo
spy.wrap do
puts "executed in wrap from foo"
yield
end
end
If you call foo without a block it will raise the exception since yield can't find a block to execute. But if you pass a block to foo method then it will be invoked:
foo do
puts "foo block"
end
Will output
executed in wrap from foo
foo block
In conclusion I think you misunderstood how yield works and I don't think it is what you want to achieve here.

Calling a block withing a block in ruby without executing the first

I am passing a block to a method for delayed execution something like
a = Proc.new do
puts "call me later"
end
Let's say I'm using this for caching expensive calls. Now lets say I wan't part of my code to run now, and part of my code to run later something like this
a = Proc.new do |c|
puts "call me later"
c.some_method do
puts "call me now"
end
end
Is it possible to get the output of "call me now" once you have the object a without calling the code to output "call me later"?
I'm not sure exactly what you're trying to accomplish, but what you have is a Proc that expects an object to be passed as a parameter, and that object has a method that accepts a block.
module ModB
def self.some_method
puts 'some_method before yield'
yield
puts 'some_method after yield'
end
end
proc_a = Proc.new do |b|
puts 'proc_a called'
b.some_method do
puts 'block called'
end
end
proc_a.(ModB)
# proc_a called
# some_method before yield
# block called
# some_method after yield
So, proc_a either needs a flag of some sort
proc_a = Proc.new do |run_me, b|
puts 'proc_a called' if run_me
b.some_method do
puts 'block called'
end
end
Or, you should be storing the block for some_method separately.
proc_a = Proc.new do
puts 'proc_a called'
end
proc_b = Proc.new do
puts 'block called'
end
proc_a.()
# proc_a called
ModB.some_method(&proc_b)
# some_method before yield
# block called
# some_method after yield

How to change self in a block like instance_eval method do?

instance_eval method change self in its block, eg:
class D; end
d = D.new
d.instance_eval do
puts self # print something like #<D:0x8a6d9f4>, not 'main'!
end
If we define a method ourself(or any other methods(other than instance_eval) which takes a block), when print self, we will get 'main', which is different from instance_eval method.eg:
[1].each do |e|
puts self # print 'main'
end
How can i define a method(which takes a block) like instance_eval?
Thanks in advance.
You can write a method that accepts a proc argument, and then pass that as a proc argument to instance_eval.
class Foo
def bar(&b)
# Do something here first.
instance_eval &b
# Do something else here afterward, call it again, etc.
end
end
Foo.new.bar { puts self }
Yields
#<Foo:0x100329f00>
It's obvious:
class Object
def your_method(*args, &block)
instance_eval &block
end
end
receiver = Object.new
receiver.your_method do
puts self #=> it will print the self of receiver
end

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