On Jan 7, 2008 1:32 AM, Christopher Smith <[EMAIL PROTECTED]> wrote:
> I'm not talking about getting rid of types. I'm talking about languages
> where the *variables* don't have types, which is a pretty common trait
> of dynamically typed languages.
>
> With a dynamically typed language, you tend not to focus on the types of
> your variables, but rather their roles (there is a difference), and of
> course the role can and should be adequately described by the variable
> name. Interestingly, knowing the roles involved in an algorithm is even
> more telling than the data types.
While convenient when cranking out code, I've found typeless arguments
to be time consuming when inheriting someone else's code. If the
method is non-trivial, I have to study the implementation carefully to
figure out what the expectations are for the argument known as, for
example, "entity". Furthermore, if I then start to rework the Entity
class, I get no compile-time help about how I just broke 12 methods in
4 files. Instead I have to run through all the test cases to find out.
And to the extent that the project's automated tests lack code
coverage, I end up producing some new bugs.
So one feature I'm contemplating in Cobra is allowing contracts speak
about typeless arguments like so:
def addEntity(entity)
require
entity responds to (get name as String)
entity responds to (def computeResults(factors))
body
...
At which point the compiler is empowered to give you some errors when
you violate the expectations of a method you're calling.
You can do this to some extent with interfaces, but there are
drawbacks. Sometimes the above is much more convenient than creating a
new interface and then visiting a dozen classes in your project to
make them conform. Also, interfaces in complex projects can get silly
where they start to cover just one method like HasName,
HasComputeResults, HasFoo, HasBar, etc. And since you cannot specify
multiple interfaces for an argument, combination interfaces might then
be created.
-Chuck
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