Explain the code block object Proc in Ruby, and explain the ruby object proc.

Explain the code block object Proc in Ruby, and explain the ruby object proc.

Proc object

Proc is a block conversion object. There are four methods to create a Proc:

Sample Code

# Method 1 inc = Proc. new {| x + 1} inc. call (2) #=> 3 # method 2 inc = lambda {| x + 1} inc. call (2) #=> 3 # method 3 inc =-> (x) {x + 1} inc. call (2) #=> 3 # Method 4 inc = proc {| x + 1} inc. call (2) # => 3

In addition to the above four types, there is also a way to convert code blocks and Proc objects through the & operator. If you want to pass a code block as a parameter to the method, you need to add the & symbol for this parameter, and its position must be at the end of the Parameter

& The meaning of the symbol is: this is a Proc object. I want to use it as a code block. Remove the & symbol to get a Proc object again.

Sample Code

def my_method(&the_proc)  the_procendp = my_method {|name| “Hello, #{name} !”}p.class  #=> Procp.call(“Bill”)  #=> “Hello,Bill”def my_method(greeting)  “#{greeting}, #{yield}!”endmy_proc = proc { “Bill” }my_method(“Hello”, &my_proc)

Notes

When using block, I will ignore the existence of proc, And I will position proc as a working person 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 new users will write code similar to the following, which will report an error,

 

 def f(..., &p)  instance_eval p end def f(..., p)  instance_eval p.call end

This is also the case,

 def f(..., &p)  instance_eval do   p.call  end end

Or

 def f(...)  instance_eval do   yield  end end

I have even written code similar to the following,

 def f(...)  instance_eval yield end

We often pass the proc object as a parameter to the method when the block is mounted, or we do not understand that & p is the block which can be directly handed over to the method for use, I have also made this mistake because I didn't distinguish block from proc correctly. & p is block, p is proc, do not explicitly create a proc unless you have to. Whenever I am confused about the relationship between block and proc, I will read a few words.