On May 21, 2008, at 11:20 PM, Johnny Lundy wrote:
You're correct - there is no first argument per se: it is part of
the method selector, together they are called a "keyword."
http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/chapter_3_section_3.html
A message with a single argument affixes a colon to the selector
name and puts the argument right after the colon. This construct is
called a keyword ; a keyword ends with a colon, and an argument
follows the colon. Thus we could diagram a message expression with a
single argument (and assignment) as the following:
****If a message has multiple arguments, the selector has multiple
keywords. A selector name includes all keywords****, including
colons, but does not include anything else, such as return type or
parameter types. A message expression with multiple keywords (plus
assignment) could be diagrammed as follows:
I should clarify my previous statement slightly in light of this
particular conceptual document.
I said:
Objective-C does not have named arguments. Nor does it have keyword
arguments.
Quite specifically, Objective-C has no notion of the arguments
arriving at the call site with any kind of labels applied to them.
That is, the sub-parts of the method name -- of the selector -- are
not optional, nor can the order be varied.
"Named arguments" and "keyword arguments" often carry the implication
that the arguments to a method can vary at runtime; can have default
values, can be in a different order, can possibly have additional
named arguments, etc... This implication would further seem to be
supported by the at-runtime method dispatch resolution featured within
Objective-C.
Yet, this is exactly *not* how Objective-C works. For all intents
and purposes, an Objective-C method declaration is simply a C function
that prepends two additional arguments; self and _cmd.
That is, this....
- (BOOL) doSomethingNeat:(NeatMode) aMode toThisThing: (Thing *) aThing;
.... is equivalent to this function...
BOOL doSomethingNeatFunc(id self, SEL _cmd, NeatMode aMode, Thing
*aThing);
... as far as the compiler type resolver is concerned. The order,
type and number of arguments is absolutely fixed (var-args being the
one exception; same rules apply as C).
This is quite distinctly different than the named or keyword arguments
available in a language like Python:
def func(a, b, NeatMode=SuperNeat, Thing=DefaultThing):
pass
Where Thing (and NeatMode) might be omitted or might have different
values when called.
b.bum
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