Table of contents
- Basic Syntax
- Relevant methods
- Ensure
- Retry
- Rescue modifier
- Exception in methods
- Multiple Exceptions
- Custom Exception
Basic Syntax
The basic syntax of ruby's exception handling looks like this.
begin
# Code that potentially raises an error
rescue => e # variable
# Execute if there was an error between begin and rescue.
end
Example
begin
raise
rescue => e
p e #=> RuntimeError
end
Relevant methods
| Method | Explanation |
|---|---|
| Object#class | Returns the class of the receiver. |
| Kernel#raise | Raise an error. |
| Exception#backtrace | Returns the backtrace of the error. |
| Exception#message | Returns the error message. |
Example
begin
raise StandardError.new("Message")
rescue => e
p e.class #=> StandardError
p e.message #=> "Message"
p e.backtrace #=> ["(repl):4:in `<main>'", "/run_dir/repl.rb:41:in `eval'", "/run_dir/repl.rb:41:in `run'", "/run_dir/repl.rb:57:in `handle_eval'", "/run_dir/repl.rb:170:in `start'", "/run_dir/repl.rb:177:in `start'", "/run_dir/repl.rb:181:in `<main>'"]
end
Ensure
You can run something regardless of the existence of an error with ensure
Example
begin
"no Error"
rescue => e
p e.message
ensure
p "Ensured" #=> Ensured
end
Example2
begin
raise StandardError.new('error')
rescue => e
p e.message #=> error
ensure
p "Ensured" #=> Ensured
end
Retry
Literally re-try the execution.
Example
file = ARGV[0]
begin
# Open a file.
io = File.open( file )
rescue
# If there was an error during opening the file, this part gets executed.
sleep( 10 )
# Goes back to begin and re-try the execution.
retry
end
Rescue modifier
You can write begin ~ rescue in one sentence just like if ~ end in Ruby.
Example
raise "Error" rescue p "rescued" #=> rescued
Exception in methods
You don't need to write begin and end to do exception handling in methods.
Example
def method
raise 'error'
rescue => e
p e.message #=> error
ensure
p 'ensured' #=> ensured
end
method #=> "error"
Multiple Exceptions
You can write rescue multiple times for each corresponding error.
begin
rescue Exception1, Exception2 => e
# For Exception1 or Exception2
rescue Exception3 => e
# For Exception3
rescue => e
# For other errors.
end
Example
begin
raise StandardError
rescue StandardError, RangeError
p 'Standard or Ranage Error'
rescue RuntimeError
p 'Runtime Error'
rescue => e
p 'some other error'
end
#=> "Standard or Ranage Error"
Custom Exception
Simply Follow the steps below.
(1) Make a new Class
class CustomError < StandardError
end
(2) Add a message
class CustomError < StandardError
def initialize(msg="My Error")
super
end
end
(3) Add custom data attributes to your exception
class CustomError < StandardError
attr_reader :atr
def initialize(msg="My Error", atr="atrribute")
@atr = atr
super(msg)
end
end
Example
class CustomError < StandardError
attr_reader :atr
def initialize(msg="My Error", atr="atrribute")
@atr = atr
super(msg)
end
end
begin
raise CustomError.new("CustomMessage", "Custom Attribute")
rescue => e
p e.message #=> "CustomMessage"
p e.atr #=> "Custom Attribute"
end
Top comments (4)
Exception handling is one of the important parts of any programming language. The basic features of exception handling have been around in Ruby since version 1.9 However, if you are not used to a strong typing language and protected mode in Ruby, you may easily miss an easier way to catch and handle exceptions. Congratulations Message For New Home
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In ruby, exception managing is a technique which describes a way to deal with the error raised in a software. Here ENGLISH LANGUAGE PROGRAM , error manner an unwanted or unexpected event, which takes place at some stage in the execution of a program, i.E. At run time, that disrupts the regular waft of this system’s instructions. So those sorts of errors have been handled via the rescue block.
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