[Newbies] Newbie: Error Checking in Dynamically typed

Language

Aditya Siram aditya_siram at hotmail.com Sun Dec 10 03:22:09 UTC 2006 wrote:

Hi all, This is my first time working with a dynamically

typed environment and my

first instinct is to error check all arguments. For

example suppose I want

to create an object to represent an octet in an IP

address (a number between

0 and 256) I would do something like this:

Object subclass: #Octet instanceVariables: 'octetValue' ......

initialize super initialize. octetValue := 0.

setOctetValue: numBtw0And256 octetValue = numBtw0And256 <-------Here's

where I have a problem

How do I know the numBtw0And256 is actually an

integer between 0 and 256 and

not 'cat' or '3.14'?

Octet>>setOctetValue: numBtw0And256 (self isOctet: numBtw0And256 ) ifTrue: [ octetValue := numBtw0And256 ] ifFalse: [ self error: 'ooch, ouch, eeach, ' , numBtw0And256 printString , ' was supposed to be an octet and it was not.' ]

Octet>>isOctet: anOctet "True iff rcvr is an octet value anOctet isInteger ifFalse: [^false ] ^(anOctet min: 256 max: 0 ) = anOctet

alternately you can define isOctet in two places

Object>>isOctet "False for anything but a small integer" ^false

SmallInteger>>isOctet isOctet "True iff rcvr is an octet value ^(self min: 256 max: 0 ) = self

and replace the predicate (self isOctet: numBtw0And256 ) with: numBtw0And256 isOctet

Since I came from statically typed languages I feel

like I writing a whole

bunch of error checking code along the lines of

ifIsInteger: ... etc which

doesn't seem to be in the spirit of Squeak.

If you don't know where your data is coming from it is good to check it. Especialy as you write new stuff. You want errors to point to themselves early. Later in refactoring you can weed out redundant test if you need to get back the speed. Squeak has had a lot of cowboys who code up stuff w/o checking or taking small steps. Squeak has a lot of bugs introduced from letting that code in. Don't let the spirit of squeak mislead you. Good programing practices are good programming practices.

Yours in service, -- Jerome Peace

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