CODEWITHSUNDEEP
grails
iberck
iberck

Reputation: 2430

Why some taglibs in Grails returns a Closure?

Why do some core taglibs in Grails return a closure? For example createLink (see source)? What are the benefits or use cases?

Upvotes: 0

Views: 57

Answers (1)

Joshua Moore
Joshua Moore

Reputation: 24776

So, what you are actually seeing is that createLink is defined as a Closure, not that it's returning a Closure when it's executed. The closure itself is executed and delegates the implementation which is responsible for the actual work of creating the StreamCharBuffer. Let's look at the source and see what's really going on:

Closure createLink = { attrs ->
  return doCreateLink(attrs instanceof  Map ? (Map) attrs : Collections.emptyMap())
}

As you can see above we have a variable called createLink of type Closure which delegates it's work to doCreateLink. Which happens to be a protected method within the containing class.

protected String doCreateLink(Map attrs) { 
  ... // actual implementation cut out of this example
  return useJsessionId ? res.encodeURL(generatedLink) : generatedLink
}

As you can see this is where the actual work is done to generate the StreamCharBuffer (Well, String, which casts nicely).

Now, why would you do this? One possible use case is, the method doCreateLink is much more strict than the closure createLink in the formal definition. By using a Closure instead of the method, the call to createLink can change slightly over time as enhancements or additions are made to it with (hopefully) little or no impact to previous uses of it.

Hopefully that helps explain a bit about what you are seeing and possibly why.

Upvotes: 3

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