W3TPL/tag/let

About

Action: Assigns a value to a variable.

This page is based on a close examination of the code as it existed on 2022-04-11, after extended debugging and reworking.

Options

• "input" = input stage (determining where the input value should come from, and retrieving it); handled by GetTagInput()
• "calc" = doing things with the retrieved input; handled by UseTagInput()
• "output: = putting the results other places besides the target variable; also handled by UseTagInput()

core

Support for this attribute is required in order for the tag to fulfill its basic purpose.

• name=: name of variable to receive the calculated value

supported

• append (calc): append the input string to the current value
• arg= (input): name of POST field to retrieve as tag input
  • USAGE: form processing
• chr= (input): ASCII number of character to use as tag input
• copy= (input): name of another variable whose value should become the input
• echo (output): display the resulting value (at the tag's location in the page)
  • This should probably be deprecated. 2022-04-11
• lcase (calc): apply strtolower(), i.e. convert the input to lower case
  • opposite of "ucase"
• lcfirst (calc): apply lcfirst(), i.e. convert the first character of the input to lower case
  • opposite of "ucfirst"
• len= (calc): use only the first <len> characters of the input (this could probably stand some rethinking)
• parse (calc): have MediaWiki parse the input, and use the resulting string
• pre (calc): alias for "parse", for backwards compatibility
• self (input): use output variable's current value as input for processing
  • e.g. for incremental operations
• self (input): takes starting value from same variable, to allow unary operations
• trim (calc): apply trim()
• ucase (calc): apply strtoupper(), i.e. convert the input to upper case
  • opposite of "lcase"
• ucfirst (calc): apply ucfirst(), i.e. convert the first character of the input to upper case
  • opposite of "lcfirst"
• val= (input): value to use as input

unsupported

These are currently not enabled. Code to support some of them exists, though it may not be working.

• index=: treats the target variable (specified by <{{{1}}}>) as an array, and specifies the element to use
• load (should probably be "fetch"): retrieve starting value from the current page's properties
  • opposite of "save"
• null: set the calculated value to NULL
• null (input): use NULL as the input
• oparse is now just "parse"
• page= (input): name of wiki page to use as input (instead of tag contents)
• raw: if present, "save" will store the value as an unserialized string
  • The default is to serialize it, preserving variable type.
  • I think this only applied to <save>.
• save (should probably be "store"): store the result in the properties for the current page
  • opposite of "load"

History

• 2011-05-31 MainProcess()/DoFromScalar(): added "tag" attribute
• 2016-09-22 MainProcess()/DoFromScalar(): adapting as method of LET tag object
• 2017-10-30 MainProcess()/DoFromScalar(): major rewrite of everything
  • changing from static to dynamic
  • using internal properties
• 2017-11-01 rewrite
  • Removing support for "load" attribute until we have a usage case.
  • It doesn't make sense to load a value you'd have to save anyway.
    • (Different page, perhaps? But when would we need that? Need usage case.)
  • (MainProcess()) copied code from DoFromScalar() to MainProcess(), which will replace it
  • replacing DoFromScalar() with MainProcess()
• 2018-06-04 This currently saves the property values in RAW format (i.e. not serialized).
  • To change this, replace SaveValueRaw() with SaveValue().
• 2020-08-17 (MainProcess()) upgrades and fixes
  • Somehow, Var::GetValue_fromExpression() wasn't being called to interpret "val=" expressions. I've reinstated it. Not sure if there are other attributes where it should be applied. If they come up, document them.
• 2020-09-24 introducing the 'raw' attribute, which saves in non-serialized format
  • Now saving serialized by default.
• 2022-04-08 Belatedly saving the figured value into the variable. Where was that being done before?
• 2022-04-09
  • MainProcess() is, uh, no longer being called...
    • STAGE 1 was replaced by GetTagInput() (input is retrieved from somewhere)
    • STAGE 2 now replaced by UseTagInput() (operations are done on the input)
  • removed DoFromScalar()