[Tcl-bugs] [ tcl-Feature Requests-1230253 ] match array

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Feature Requests item #1230253, was opened at 2005-06-30 11:07
Message generated for change (Comment added) made by dkf
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Category: 18. Commands M-Z
Group: None
>Status: Deleted
Resolution: Rejected
>Priority: 1
Submitted By: Markus Elfring (elfring)
Assigned to: Donal K. Fellows (dkf)
Summary: match array

Initial Comment:
http://tcl.tk/man/tcl8.5/TclCmd/regexp.htm:
I want that matches can be stored into an array instead 
of "subMatchVars".
I imagine cases where I can not use finite and 
predefined variable names because the search pattern 
was dynamically constructed.

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>Comment By: Donal K. Fellows (dkf)
Date: 2005-07-03 20:44

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To reaffirm: requested feature can be implemented using a
Tcl procedure, and adding it to the core is a fair bit of
effort which would be better spent elsewhere. All
significant costs can be worked around in one way or another
with existing facilities.

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Comment By: miguel sofer (msofer)
Date: 2005-07-02 20:02

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The variable name "-" is just a mnemonic for "a variable
that I actually do not care about, and will not be
dereferencing".

As to the performance win: trust me, it is not there in any
simple implementation. It will actually be slower. It could
be made marginally faster, at a complexity cost that is way
beyond reasonable.

Returning the ticket to dkf, as (a) this is not my area and
(b) he did claim it. Please do not alter maintainer
assignments arbitrarily.

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Comment By: Markus Elfring (elfring)
Date: 2005-07-02 19:30

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What is your intention with the use of the variable name "-"?

Well, I guess that this kind of loop for the conversion from
a list to an array can be more efficiently implemented in C
code. I assume that there are speed improvements and reduced
memory consumption possible because the value copies to the
variables (key, val) can be avoided in the internal processing.

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Comment By: miguel sofer (msofer)
Date: 2005-07-02 14:36

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I still do not quite get it. I think you are proposing to
have a builtin capability to do something like

foreach {- key val} [regexp -all -inline $pattern $source] {
    set vector($key) $val
}

What should happen if the pattern does not always produce an
even number of submatches? Would that be an error? What if
the pattern is capable of producing an odd number of
submatches, but doesn't with the particular input : error or
not?

As it is, I do not think the complication is really worth
it. You can easily get this functionality in a proc. It is
quite unlikely that the performance impact will be
noticeable, if this is what is worrying you: proc calls and
[set] are quite a bit faster than [regexp] in any case.

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Comment By: Markus Elfring (elfring)
Date: 2005-07-02 08:45

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How do you think about this use case?
I imagine the following function calls to import mapping
tables into corresponding data structures.

set source1 {Pi/3.1415,Tax/0.16,}
set pattern1 {([^/]+)/(.+),}
regexp -all -array vector1 $pattern1 $source1
regexp -all -list contents1 $pattern1 $source1
set source2 {1-title:23-name:456-address:}
set pattern2 {([^\-]+)-(.*):}
regexp -all -type array -param vector2 $pattern2 $source2
regexp -all -type list -param contents2 $pattern2 $source2

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Comment By: miguel sofer (msofer)
Date: 2005-07-01 23:57

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Correcting a bad typo in my last comment here: "... my
opinion is that the core should NOT be doing it for you."

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Comment By: Donal K. Fellows (dkf)
Date: 2005-07-01 22:57

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I see no need for such a thing.

Quite apart from the -inline option described by Miguel, the
-about option returns (among other things) the maximum
number of subMatchVars required by a particular RE, so
allowing for the construction of a command to perform the
matching and place the submatches directly into any
variable(s) chosen. This means that this would all be
syntactic sugar at best (and is, of course, easily simulated
using a procedure).

(Maintainer Note: The [regexp] command, as opposed to the RE
guts, is in Category 18)

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Comment By: miguel sofer (msofer)
Date: 2005-07-01 17:14

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I do not fully understand the spec for your request: what
would be the array keys for the different matches? 

If it is the order in which they are found, the list result
is the correct format - just access themby [lindex], or
[foreach]. Or convert to an array if you think you must. In
that case, my opinion is that the core should be doing it
for you.

If the array keys are something else (maybe some part of the
regular expression itself?), maybe ... Although it is not at
all clear to me yet how we could do this.

Can you please provide an example of what would happen if
this feature is implemented?

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Comment By: Markus Elfring (elfring)
Date: 2005-07-01 17:03

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Well, it can be one way for a solution.
Can the extra conversion step of this list into an array be 
avoided?
(Each data type has got its own advantages.)

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Comment By: miguel sofer (msofer)
Date: 2005-06-30 12:01

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Doesn't the '-inline' option provide what you need? It
returns the matches in a list.


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