Is there an invisible-parent tag collection object available?

[X]

Is there something like an invisible tag container object/collection?

I'm looking for this for the following problem: how to render multiple elements that are under a condition?

Example, I would like to output:

<div>
  <span>info</span>
  ,<span>delete</span>
</div>

where this part is optional:

,<span>delete</span>

(only moderators can see ", delete")

How can I code this in Scalatags? The following doesn't work:

div(
  span("info"),
  if (isModerator) ", " + span("delete") else ""
)

because this causes the if-body to be seen as a String (instead of a Scalatags structure) and thus be escaped by ScalaTags.

The only solution that I currently have is:

div(
  span("info"),
  if (isModerator) raw(" ," + span("delete").toString) else ""
)

But the "raw" and "toString" part feel a bit uncomfortable.

Is there something like this?:

div(
  span("info"),
  if (isModerator) List(" ,", span("delete")) else ""
)

that would be cleaner in my opinion.

[X]

This does work, but a bit verbose with the type parameter "Modifier"

div(

  span("info"),

  if (isModerator) List[Modifier](" ,", span("delete")) else ""

)

But couldn't get the code compiling yet using something like this:

object STList {

  def apply(elements: Modifier*): List[Modifier] = {

    List[Modifier](elements: _*)

  }

}

div(

  span("info"),

  if (isModerator) STList[Modifier](" ,", span("delete")) else ""

)

Op dinsdag 30 december 2014 14:12:46 UTC+1 schreef X:

[X]

I was using the wrong Modifier in the previous solution. This one works:

import scalatags.Text.all.Modifier

object STList {

  def apply(elements: Modifier*): List[Modifier] = {

    List[Modifier](elements: _*)

  }

}

div(

  span("info"),

  if (isModerator) STList(" ,", span("delete")) else ""

)

Is this the preferred way to use Scalatags?

Op dinsdag 30 december 2014 14:12:46 UTC+1 schreef X:

Is there something like an invisible tag container object/collection?

[re...@reactific.com]

What works for me is a construct like:

if (condition) Seq(modifiers) else Seq.empty[Modifier]

That is actually so commonplace that we might want to make something like this

object conditional {
  def apply(cond: => Boolean, value: Modifier*) {
    if (cond) value.toSeq else Seq.empty[Modifier]
  }
}

I imagine this could be used like:

div("span("info"), conditional(isModerator, ",", span("delete")))

Would something like that work?

Please note: I haven't compiled the above, just wrote it off the top of my head so please forgive any typos/errors.

Reid.

[Haoyi Li]

In the latest master () is now an invisible marker; otherwise Seq.empty or None or "" work too

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[X]

What works for me is a construct like:

if (condition) Seq(modifiers) else Seq.empty[Modifier]

I'm getting a compile error when using Seq without type parameters:

  div(

    span("info"),

    if (condition) Seq(", ", span("delete")) else ""

  )

error:

type mismatch;

[error]  found   : Seq[java.io.Serializable]

[error]  required: scalatags.Text.Modifier

[error]     (which expands to)  scalatags.generic.Modifier[scalatags.text.Builder]

[error]           if (isAdmin) Seq(", ", a(href:=psetEditLink)("edit")) else ""

although is does work with type parameter (Seq[Modifier](.....)), but that's similar to my List[Modifier] solution, which both are a bit verbose because of the type parameter. The STList solution does work without type parameter. 

The conditional object solution works fine (") {" has to be changed to ") = {").

[X]

Seq(modifiers)

doesn't seem to work. I have to add a type parameter:

Seq[Modifier](modifiers)

But it would be better to shield users from ScalaTag internals such as "Modifier", right?

Although the "conditional" object solution does work. (Note that ") {" has to be changed to ") = {".)

But I think there are still situations in which even without conditionals, there's a need for a grouping/collection element like Seq but without type parameters.

[Haoyi Li]

I don't consider Modifier to be internal; I'd say Modifier and Frag are user-facing types. Maybe we could figure out a way to make the type inference work better though. I don't fully grok the intricacies of type inference in scalac, as is evidenced by issues like https://github.com/lihaoyi/scalatags/issues/16

[Byron Weber Becker]

+1 on this request.  For another usage you need look no further than the ScalaTags documentation.  We all know that builtin tags can take a sequence of tags as children.  For example,

```div(p("one"), p("two"))```

However, if a user wants to write a function that does the same we need to write (see the documentation under "Layout")

```def page(scripts: Seq[Frag], content: Seq[Frag]) =...```

and then explicitly wrap the fragments as a sequence.  It would be really nice to be able to avoid that Sequence -- the the mental overhead of knowing when you need to wrap things as a sequence and when you don't.

The problem I'm banging my head on right now is similar page, except that I expect its usage to be much more frequent.  Therefore, I'm trying to make it "nice" but feel like I keep getting hung up on passing a sequence of tags to it.

Byron