Detailed code block objects in Ruby Proc_ruby topics

Proc Objects

Proc are objects that are converted by blocks. There are four ways to create a proc, respectively:

Sample code

# Law one
inc = Proc.new {| x | x + 1}
Inc.call (2) #=> 3

# method two
inc = Lambda {| x | x + 1}
Inc.call (2) # => 3

# method three
inc =-> (x) {x + 1}
Inc.call (2) #=> 3

# method four
inc = proc {|x| x + 1}
Inc.call (2) #=> 3

In addition to the above four, there is a way through the & operator, the code block and proc object conversion. If you need to pass a code block as a parameter to a method, you need to add a & symbol to the parameter, and its position must be at the last

The meaning of & symbol is: This is a proc object, I want to use it as a block of code. Remove the & symbol and get a proc object again.

Sample code

def my_method (&the_proc)
  the_proc
end

p = my_method {|name| "Hello, #{name}!"}
P.class  #=> Proc
p.call ("Bill")  #=> "Hello,bill"


def my_method (greeting)
  "#{" Greeting}, #{yield}! "
End

My_proc = proc {"Bill"}
My_method ("Hello", &my_proc)

Some places to be aware of

When using block, I will ignore the existence of proc, and I will position proc as a worker behind the scenes. I often write code similar to the following

 def f (...)
  ...
  Yield ...
 End

 def f (..., &p)
  ...
  P.call ...
 End

 def f (..., &p)
  instance_eval &p
  ...
 End

 def f (..., &p)
  ...
  Defime_method m, &p ...
 End

Some beginners will write code similar to the one in which the following execution will report an error.

 Def f (..., &p)
  instance_eval P end

 def f (..., p)
  instance_eval p.call
 End

There is also this written,

 Def f (..., &p) instance_eval do
  P.call end
 

Or

 def f (...)
  Instance_eval do
   yield
  end
 

I even wrote code similar to the following

 def f (...)
  Instance_eval yield End
 

We often have to hang block, but the proc object when the argument to the method, or do not understand &p is block can be directly to the use of methods, I have made such a mistake is because the block and proc the correct distinction between, & P is block, P is proc, do not explicitly create proc without the last resort, I will read a few words when I am confused about the relationship between Block and Proc.