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provide

{@provide [optional parameters] }blocks{/provide}

Provide rich parameter definitions

There are a number of cases where you may want to define a value for a parameter to be more complex than just the basic forms allowed by dust; viz p="abc", p=xyz, p="{xyz}". A very common case is to want the value from a helper function like {@size} that you can pass to a partial or test. @provide lets you capture that value and reference it like a parameter.

The general form of @provide is

    {@provide [optional params]}
      main block of dust
      {:block1}
        evaluation of this block defines a param named "block1"
      {:block2}
        evaluation of this block defines a param named "block2"
      ... as many blocks as you need params
    {/provide} 

Rules:

• The text in a param block must evaluate to a valid JSON object. constants, strings, array [ ], object { } are the main legal forms.
• a param on the @provide helper can be used in the main block and all param blocks
• params defined by the blocks can be used in the main block
• If a block name duplicates a param name, the block name overrides in the main block although the param can be used in the block param definitions

Examples:

Find the size of an array and pass the value to a partial
{@provide}
  {>partial size=len /}
{:len}
  {@size key=array /}
{/provide}

Create an ad hoc list of month numbers for a dropdown without the controller supplying them
{@provide selected=chosen}
  <select name="months">
    {#months}
      <option value="{.}"{@if cond="'{selected}' == '{.}'"} selected="selected"{/if}>{.}</option>
    {/months}
  </select>
{:months}
  [1,2,3,4,5,6,7,8,9,10,11,12]
{/provide}

Create an ad hoc structure to pass to a partial that expects a particular structure
{@provide}
  {>displayAddress data=struct}
{:struct}
  {"street":"{homeStreet}", "city":"{homeCity}", "state": "{homeState}" }
{/provide}