Peter MacDonaldRobert Seeger$Revision: 1.12 $

The TIP proposes the addition to two new subcommands to the array command: incr and value. The 'incr subcommand would increment an element in an array. The value subcommand would query, reference, and/or initialize an array element.

proposed modifying the incr command to auto-initialize variables which do not exist, rather than throwing an error. After some debate, it was identified that frequency counting in arrays was the primary area of interest. In particular, the excessive use of if/info exists constructs in such code is inefficient, verbose and rather difficult to read. The addition of these two subcommands could substantially reduce the complexity of much Tcl code.

Two new subcommands will be added to array, being incr and value. Both commands take an array name and an elem parameter, but, no string match is performed on elem. array incr var elem ?value? ?init? The array incr subcommand would increment var(elem), if it exists, by value, otherwise, initializes it to init. The default for value is 1, and the default for init is 0. The subcommand will return the new value and will support both integer and double values (based on the rules for addition in expr). array value var elem ?value? ?init? The array value would just return the current contents of var(elem) if it exists, or value otherwise. If the init parameter resolves to true (as determined by Tcl_GetBooleanFromObj() of course), the variable is initialized to value if it doesn't already exist. The default for value is the empty string, and the default for init is false.

Following is a Tcl only implementation of the incr/value subcommands: cHJvYyBBcnJheSB7Y21kIHZhciBlbGVtIHthbXQge319IHtpbml0IDB9fSB7ICAgIyBJbXBsZW1lbnQgdGhlIEFycmF5IHN1YmNtZHMgaW5jciBhbmQgdmFsdWUgb24gdmFyKGVsZW0pOg==ICAgIyAgLSBpbmNyICAgaW5jcmVtZW50IGEgdmFyaWFibGUgYnkgYW10IG9yIGluaXRpYWxpemU=ICAgIyAgICAgICAgICAgdG8gaW5pdCBpZiB1bmRlZmluZWQuICAgIyAgLSB2YWx1ZSAgcmV0dXJuIHRoZSB2YWx1ZSBpZiBkZWZpbmVkLCBlbHNlIHJldHVybiBhbXQ=ICAgIyAgICAgICAgICAgaW5pdGlhbGl6aW5nIGlmIGluaXQuICAgdXB2YXIgJHZhciB1dmFyICAgaWYge1tzdHJpbmcgbWF0Y2ggJGNtZCogaW5jcl19IHs=ICAgICAgaWYgeyRhbXQgPT0ge319IHsgc2V0IGFtdCAxIH0=ICAgICAgaWYge1tpbmZvIGV4aXN0cyB1dmFyKCRlbGVtKV19IHs=ICAgICAgICAgcmV0dXJuIFtzZXQgdXZhcigkZWxlbSkgW2V4cHIgeyR1dmFyKCRlbGVtKSskYW10fV1dICAgICAgfQ==ICAgICAgcmV0dXJuIFtzZXQgdXZhcigkZWxlbSkgJGluaXRdICAgfSBlbHNlaWYge1tzdHJpbmcgbWF0Y2ggJGNtZCogdmFsdWVdfSB7ICAgICAgaWYge1tpbmZvIGV4aXN0cyB1dmFyKCRlbGVtKV19IHs=ICAgICAgICAgcmV0dXJuICR1dmFyKCRlbGVtKQ==ICAgICAgfQ==ICAgICAgaWYgeyRpbml0fSB7ICAgICAgICAgcmV0dXJuIFtzZXQgdXZhcigkZWxlbSkgJGFtdF0=ICAgICAgfQ==ICAgICAgcmV0dXJuICRhbXQ=ICAgfSBlbHNlIHs=ICAgICAgZXJyb3IgInVzYWdlOiBBcnJheSBpbmNyfHZhbHVlIHZhciBlbGVtID9hbXQ/ID9pbml0PyI=ICAgfQ==fQ==

Wangnic notes:array value var elem "" false can be written as array get var elemArray get returns name/value pairs. Array value returns just the value. Also if elem has a * in it, there may be multiple matches.Hobbs notes: already rejected array valuesA single item is returned from array value, not a list, as there is no string match on elem.The problem domain is not list processing (which is expected to be relatively expensive), but rather frequency counting and set matching.RHSeeger notes:It would seem more consistant to push for the incr command to include a way to initialize a variable if it doesn't exist (as per or the discussed options contained therein), rather than add an incr subcommand to array.Being a fan or reintroducing the array values TIP (since the core mailing list indicates it was never fully rejected), I think array value might be a bit confusing, being only off by the lack of plurality. (I was one of the people pushing for though, so take that aspect with a grain of salt)

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