Boolean emptiness property for arrays

[slavaschmidt]

Describe the feature

Please provide a way to conditionally render parts of the template where the condition is emptiness / non-emptiness of the list.

Use Case

When rendering lists as HTML, more often than not, it is needed to render parts of the layout only if there are some elements in the list, for example:

• Table header and/or footer are only to be shown when there are rows in the table
• Heading has to be visible only if there are paragraphs
• Ordered and unordered lists might have an introduction and/or conclusion that only need to be shown if there are elements in the list

Proposed Solution

There are two possible ways to implement this functionality:

• provide a synthetic property depending on the list emptiness, for example, when reading json. This gives full flexibility how the new key should be named
• On the tokenizer level by extending the meaning of positive and negative sections for lists:

<+list>
<h1>Currenty on vacation</h1>
<ul>
<*list><li>{{.}}</li></list>
</ul>
</list>
<-list>Nobody is no vacation now</list>

The second way feels more elegant and will work for manually constructed data models as well.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

0.2.0

Environment details (OS name and version, etc.)

any

[slavaschmidt]

Actually, the meaning of positive and negative sections could also be extended to maps, with the same meaning, checking for emptiness.

[hungrybluedev]

Implemented in 80e349f

@slavaschmidt Can you please add a sample usage in README and readme_test.v?

[slavaschmidt]

The list is covered. I believe it might be better to wait for a possibility to iterate over maps to create a meaningful example involving map (non) emptiness.

[hungrybluedev]

Emptiness checking implemented for maps and lists so that they may act like Boolean sections.