# Exceptions in initialize()? **URL:** \ **Category:** ruby-talk\ **Created:** [20 May 2003 06:30 UTC](https://rubytalk.org/t/exceptions-in-initialize/6059 "2003-05-20T06:30:58Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Jack\_Twilley](https://avatars.discourse-cdn.com/v4/letter/j/e47c2d/32.png) [@Jack\_Twilley](https://rubytalk.org/u/Jack_Twilley)\ **Post date:** [20 May 2003 06:30 UTC](https://rubytalk.org/t/exceptions-in-initialize/6059/1 "2003-05-20T06:30:58Z")
I’m very new to ruby, so please be gentle. I have created a class and an initialize() method. I would like an attempt to initialize() to fail if either an argument is not supplied or the supplied argument does not match a regular exponent. The solution would appear to be to use an exception, but I cannot tell - From the documentation what happens if an exception is thrown from within an initialize() method and not caught. I know I can “just try it”, but I’m interested in knowing what’s supposed to happen in that case. I’m hoping that what is supposed to happen is that the new object is equal to nil, but I can’t be sure of the defined behavior until it’s defined. Thank you for your patience and assistance. Jack. * * * Jack Twilley jmt at twilley dot org http colon slash slash www dot twilley dot org slash tilde jmt slash ---
**Author:** ![Mauricio\_Fernndez](https://avatars.discourse-cdn.com/v4/letter/m/e495f1/32.png) [@Mauricio\_Fernndez](https://rubytalk.org/u/Mauricio_Fernndez)\ **Post date:** [20 May 2003 07:05 UTC](https://rubytalk.org/t/exceptions-in-initialize/6059/2 "2003-05-20T07:05:14Z")
> I’m very new to ruby, so please be gentle. > > I have created a class and an initialize() method. I would like an > attempt to initialize() to fail if either an argument is not supplied > or the supplied argument does not match a regular exponent. The > solution would appear to be to use an exception, but I cannot tell > > - From the documentation what happens if an exception is thrown from > within an initialize() method and not caught. > > I know I can “just try it”, but I’m interested in knowing what’s > supposed to happen in that case. I’m hoping that what is supposed to > happen is that the new object is equal to nil, but I can’t be sure of > the defined behavior until it’s defined. > > class Foo; def initialize; raise “foo”; end; end > > =\> nil > > a = Foo.new rescue nil > > =\> nil > > a > > =\> nil or > > def Foo.new(\*args) > > begin > > ?\> super(\*args) > > rescue > > nil > > end > > end > > =\> nil > > a = Foo.new > > =\> nil > **···** > > On Tue, May 20, 2003 at 03:30:58PM +0900, Jack Twilley wrote: > > – > \_ \_ > > > > \_\_ \_\_ _| |_ \_\_\_ \_ \_\_ \_\_\_ \_\_ \_ \_ \_\_ > > > '\_ \ / _`| __/__ | '_` \_ \ / ` | ’ \ > > > ) | (| | |_\_\_ \ | | | | | (_| | | | | > > > .\_\_/ \_,_|\ __|__ /| |_| |_|\__,_|_| |\_| > > > Running Debian GNU/Linux Sid (unstable) > > > batsman dot geo at yahoo dot com > > There are 3 kinds of people: those who can count & those who can’t. > – Unknown source ---
**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\ **Post date:** [20 May 2003 07:31 UTC](https://rubytalk.org/t/exceptions-in-initialize/6059/3 "2003-05-20T07:31:29Z")
“Jack Twilley” [jmt+usenet@twilley.org](mailto:jmt+usenet@twilley.org) schrieb im Newsbeitrag [news:86u1bqi18y.fsf@duchess.twilley.org](mailto:news:86u1bqi18y.fsf@duchess.twilley.org)… -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I’m very new to ruby, so please be gentle. I have created a class and an initialize() method. I would like an attempt to initialize() to fail if either an argument is not supplied or the supplied argument does not match a regular exponent. The solution would appear to be to use an exception, but I cannot tell - From the documentation what happens if an exception is thrown from within an initialize() method and not caught. I know I can “just try it”, but I’m interested in knowing what’s supposed to happen in that case. I’m hoping that what is supposed to happen is that the new object is equal to nil, but I can’t be sure of the defined behavior until it’s defined. ``` Yes, it's nil because the assignment didn't take place. But typically ``` this is not too interesting since the code following the assignment will not be executed anyway: irb(main):001:0\> class Foo irb(main):002:1\> def initialize(a) irb(main):003:2\> raise “should’ve been ‘a’” unless “a” == a irb(main):004:2\> @a=a irb(main):005:2\> end irb(main):006:1\> end nil irb(main):007:0\> irb(main):008:0\* f1 = Foo.new “a” #\ irb(main):009:0\> irb(main):010:0\* Thread.new do irb(main):011:1\* f2 = Foo.new "b" irb(main):012:1\> puts "never here" irb(main):013:1\> end #\ irb(main):014:0\> irb(main):015:0\* p defined? f3 nil nil irb(main):016:0\> irb(main):017:0\* begin irb(main):018:1\* f3 = Foo.new "b" irb(main):019:1\> puts "never here" irb(main):020:1\> rescue =\> e irb(main):021:1\> p e irb(main):022:1\> end #\ nil irb(main):023:0\> irb(main):024:0\* p defined? f3 "local-variable" nil irb(main):025:0\> ``` robert ```