On Mon, 03 Aug 2009 07:04:52 -0400, Michel Fortin
<michel.for...@michelf.com> wrote:
On 2009-08-02 23:19:50 -0400, "Robert Jacques" <sandf...@jhu.edu> said:
On Sun, 02 Aug 2009 20:53:35 -0400, Michel Fortin
<michel.for...@michelf.com> wrote:
On 2009-08-02 20:18:51 -0400, "Robert Jacques" <sandf...@jhu.edu> said:
I also like the idea of omitting parenthesis for functions with no
argument.
I like it too. But the problem with the current approach D are:
1. A syntax that permits function to be called both without and with
empty parenthesis creates ambiguities when it returns a callable type
(a delegate or an object with an opCall member).
2. We want properties to be nouns, and actions to be verbs. In
english a lot of words are both nouns and verbs, which makes it
impractical to distinguish a property from a function by its name
alone.
Solving 1 involves having a way to say functions that can and must
be called without parenthesis. Unless we want to force all functions
with no parameter to be called without "()", we must have some kind
of flag to tell us that a function expects or does not expect "()".
Solving 2 involves making a difference in the call syntax between
property and action functions. Since the idea behind a property is to
mimic a field, it follows that the best differentiator for properties
is the lack of parenthesis.
I'd be glad too if we could continue to skip parenthesis for calls
to functions with no arguments, but I think fixing the two problems
above is more important.
I agree 1) is an issue, but I view it as a corner case. (I use
zero/one arg functions all the time and make use of the 'property'
syntax left right and center, but I've never run into the opCall
problem) It would be nice if it were fixed, but we may be cutting off
the nose to spite the face, as it were. (Or alternatively, taking the
scientific instead of engineering approach)
Problem 2) I think is a major logical flaw: a property is a function.
So I see no need to distinguish between the two. Properties, in fact,
can be a very expensive functions that takes locks/do database
lock-up/etc. So making syntax changes that make 'properties' look
cheap and 'functions' look expensive is worse than what we have today.
Today, at least, everyone knows that no parenthesis doesn't mean
necessarily cheap O(1) operation.
And I agree with you: properties are functions. But problem number 2
isn't about whether properties are functions or not. It's about the
meaning of a name. Say you have a "transform" function, you'll have some
expectations about what it does based on the name. So I ask you: is a
"transform" function an *action* (a verb) in the sense that it applies
some transformation to an object, or is it a *property* (a noun or
adjective) in the sense that it returns something like an affine
transform associated with an object? The semantics of the two are
completely different, yet they share the same name.
The real ambiguity here is the English language, were many nouns and
adjectives are also verbs. We could switch to a natural language that
does not have this problem for function name -- say French: "transform"
becomes "transformer" (action, verb) or "transformation" (property,
noun); "empty" becomes "vider" (action, verb) or "vide" (property,
adjective) -- but that doesn't seem like a very practical option.
So, beside switching to a non-English language, we have two other
options. First we could write a guideline saying properties (nouns and
adjectives) should start with some prefix. I tried it[1]. I couldn't
come with anything sane that works for non-boolean properties. In
addition, most people don't read guidelines, and educating people to
write "is", "has" or a modal verb in front of boolean properties would
be a major effort. It works in Objective-C, but Objective-C function
naming conventions are very different.
[1]: http://prowiki.org/wiki4d/wiki.cgi?DProgrammingGuidelines
So the only option left, assuming we still want to solve the problem, is
to introduce a formal syntax in D to distinguish properties (nouns and
adjectives) from actions (verbs). A natural fit for that at the call
site is to use the syntax without tailing empty parenthesis for
properties, mimicking fields, and use the inherited function syntax from
C-derived languages for actions. Choosing the right syntax for property
definitions is a greater challenge since we want a simple syntax that
helps people make the right choice depending on wether they want a
property or an action, but we (Andrei, me, some others) don't want to
deviate too much from a regular function either.
As for whether properties should be cheap (not perform anything
heavyweight) or not, that's another debate result in a guideline.
Thank you for the very elegant expression of the problem and for posting
the programming guidelines wiki. My criticism is that you're defining your
context to narrowly. A function/property/field isn't just defined by it's
name, but also by it's type and the context it's in. A 'transform' of type
void or typeof(this) is obviously an action, while a 'transform' of type
Matrix might be a coordinate frame. The object's type also conveys context
information; a 'transform' on an autobot might be an action, while a
'transform' on it's 3D model might be a coordinate frame. Even if you
don't know the return type off the top of you're head (i.e. you're doing a
code review), 'transform;' or 'object.transform;' are obviously actions
while 'auto a = object.transform;' or 'object.transform = a' is a noun.
English solves it language ambiguity issues with context, so why can't the
same solution apply to programming languages? Sure, pathological examples
are possible, just as they're possible in English, but that's no reason to
switch to a different language.
