[Tcl-bugs] [ tcl-Feature Requests-745851 ] [dict merge]

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Feature Requests item #745851, was opened at 2003-05-30 02:15
Message generated for change (Comment added) made by dkf
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Category: 15. Dict Object
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Joe English (jenglish)
Assigned to: Donal K. Fellows (dkf)
Summary: [dict merge]

Initial Comment:


A useful addition to [dict] would be a command that

sets multiple dictionary entries in a single step:



dict merge $dictval1 $dictval2 ? ... $dictvalN ?



which would return a copy of $dictval1, extended or

modified by the values in $dictval2.  If multiple

arguments are supplied, values in later arguments

override those in earlier ones.



That is:



proc dict_merge {dict1 args} {

     foreach dict $args {

        foreach {key value} $dict {

            dict set $dict1 $key $value

        }

     }

    return $dict1

}



(This was discussed on tcl-core, but the vote on TIP

111 was already in progress so it didn't make it into

the initial implementation.)



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>Comment By: Donal K. Fellows (dkf)
Date: 2003-09-06 21:16

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Good use case.  Just what I wanted. I'd be happy to support

a TIP.



(I'm less certain about the C interface.  Merging is a

pretty trivial thing to do with the current C API after all.)

----------------------------------------------------------------------

Comment By: Joe English (jenglish)
Date: 2003-09-06 02:48

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(Let's see if SourceForge is working today...)



Attached patch implements [dict merge].  Documentation and

test cases still missing.



This might also be a useful thing to have in the C

interface, should refactor.



PS: for a real-live, actual use case, see  'proc myReturn'

in the EXAMPLES section of return.n (r1.7), which currently

uses:



    set options [eval [list dict create -level 1] $args]



This could be replaced with



   set options [dict merge {-level 1} $args]





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Comment By: Joe English (jenglish)
Date: 2003-05-30 18:42

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> would using C for this purpose be a significant

advantage?  

> It increases the maintenance load, after all...



So that it could be spelled [dict merge] instead of

[dict_merge] :-).  There are minor efficiency issues as

well.



But mostly, this is a useful primitive operation on

dictionaries that (I feel) should be part of the core

interface.

----------------------------------------------------------------------

Comment By: Donal K. Fellows (dkf)
Date: 2003-05-30 09:48

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A better implementation might go like this:



proc dict_merge {dict1 args} {

   foreach dict $args {

      dict for {key val} $dict {

         dict set dict1 $key $val

      }

   }

   return $dict1

}



However, would using C for this purpose be a significant

advantage?  It increases the maintenance load, after all...

----------------------------------------------------------------------

Comment By: Joe English (jenglish)
Date: 2003-05-30 02:17

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[dict merge] can also be expressed as:



    [eval dict replace [list $dict1] $dict2 ... $dictN]



but I'd prefer a solution that doesn't involve [eval].



A variant form that operates on dictionary variables would

also be useful (don't know what to call it though.)

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