[ET Trac] [Einstein Toolkit] #1220: OPTIONAL_IFACTIVE

[Einstein Toolkit]

#1220: OPTIONAL_IFACTIVE
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 Reporter:  eschnett     |       Owner:     
     Type:  enhancement  |      Status:  new
 Priority:  major        |   Milestone:     
Component:  Cactus       |     Version:     
 Keywords:               |  
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 Following up on a discussion on the Cactus developers mailing list, I want
 to suggest a third way of indicating a desired capability. In addition to
 REQUIRES and OPTIONAL, I suggest OPTIONAL_IFACTIVE. This behaves like
 OPTIONAL, except that the capability relationship only exists if the thorn
 providing the capability is active.

 For example, thorn GRHydro would state "OPTIONAL_IFACTIVE Carpet". This
 mean that, if Carpet is built into the configuration (i.e. is in the thorn
 list), _and_ if Carpet is active, then GRHydro will depend on it, e.g. by
 calling functions in Carpet. If Carpet is not in the thorn lists, these
 calls will be #ifdef'd out, and if Carpet is not active, these calls will
 not occur.

 This will make it possible to automatically activate all thorns that
 provide a required capability. In fact, the attached patch already
 implements this.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1220>
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