[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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