Re: Default arguments

[Dmitri A. Sergatskov]

On 12/15/06, Sean O'Rourke <address@hidden> wrote:
> My bad.
>
> /s
>
> -----------------------------------------------------------------
>
> Please reply on the list so the discussion is kept archived and public
> for others to comment.
>
> Thanks,
>
> jwe
>
> On 15-Dec-2006, Sean O'Rourke wrote:
>
> | "John W. Eaton" <address@hidden> writes:
> | > One problem I have with keyword arguments is that if they are
> | > allowed for any function argument, then you have to carefully
> | > choose the names of all function parameters, and once you've
> | > selected them, you can't change them without the potential for
> | > breaking a lot of code.
> |
> | This is a significant constraint on library code (octave and
> | octave-forge), but within your own code it seems manageable, and
> | these kinds of interface decisions should be finalized before
> | code is widely distributed.  I haven't had much trouble either
> | with Lisp or with the current "'key', value" approach in Octave.
> |
> | > There would also be problems with the way variable arguments
> | > are overloaded in some Matlab functions.
> |
> | I would propose that only arguments with default values can be
> | passed using keywords, since non-optional keyword arguments are
> | just strange.  That way there's no impact on existing functions.
> |
> | /s

This all starting to remind me IDL, that has both positional and keyword
parameters for functions and procedures. Here is a snip from its manual:

<<<<
The correspondence between the actual parameters of the caller and the
formal parameters of the called procedure is established by position
or by keyword.

Positional Parameters (Arguments)

A positional parameter, or plain argument, is a parameter without a
keyword. Just as its name implies, the position of a positional
parameter establishes the correspondence—the n-th formal positional
parameter is matched with the n-th actual positional parameter.

Keyword Parameters

A keyword parameter, which can be either actual or formal, is an
expression or variable name preceded by a keyword and an equal sign
("=") that identifies which parameter is being passed.
When calling a routine with a keyword parameter, you can abbreviate
the keyword to its shortest, unambiguous abbreviation. Keyword
parameters can also be specified by the caller with the syntax
/KEYWORD, which is equivalent to setting the keyword parameter to 1
(e.g., KEYWORD = 1). The syntax /KEYWORD is often referred to, in the
rest of this documentation, as setting the keyword.
For example, a procedure is defined with a keyword parameter named TEST.
PRO XYZ, A, B, TEST = T
The caller can supply a value for the formal (keyword) parameter T
with the following calls:
; Supply only the value of T. A and B are undefined inside the
; procedure.
XYZ, TEST = A

; The value of A is copied to formal parameter T (note the
; abbreviation for TEST), Q to A, and R to B.
XYZ, TE = A, Q, R

; Variable Q is copied to formal parameter A. B and T are undefined
; inside the procedure.
XYZ, Q
result = FUNCTION(Arg1, Arg2, KEYWORD = value)

> > > >

FYI

Dmitri.
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