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From: neykov <git@git.apache.org>
To: dev@brooklyn.apache.org
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References: <git-pr-462-brooklyn-server@git.apache.org>
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Subject: [GitHub] brooklyn-server pull request #462: Inherit config default values
Content-Type: text/plain
Message-Id: <20170106174248.1A488DFCB6@git1-us-west.apache.org>
Date: Fri,  6 Jan 2017 17:42:48 +0000 (UTC)
archived-at: Fri, 06 Jan 2017 17:42:50 -0000

Github user neykov commented on a diff in the pull request:

    https://github.com/apache/brooklyn-server/pull/462#discussion_r94961073
  
    --- Diff: core/src/main/java/org/apache/brooklyn/core/objs/BasicSpecParameter.java ---
    @@ -404,7 +431,126 @@ public static void addParameters(AbstractBrooklynObjectSpec<?, ?> spec, List<? e
                 spec.parametersAdd(BasicSpecParameter.fromSpec(loader.getManagementContext(), spec));
             }
             if (explicitParams.size() > 0) {
    -            spec.parametersAdd(explicitParams);
    +            spec.parametersReplace(resolveParameters(explicitParams, spec.getParameters(), spec));
    +        }
    +    }
    +
    +    /** merge parameters against other parameters and known and type-inherited config keys */
    +    static Collection<SpecParameter<?>> resolveParameters(Collection<? extends SpecParameter<?>> newParams, Collection<? extends SpecParameter<?>> existingReferenceParamsToKeep, AbstractBrooklynObjectSpec<?,?> spec) {
    +        Map<String,SpecParameter<?>> existingToKeep = MutableMap.of();
    +        if (existingReferenceParamsToKeep!=null) {
    +            for (SpecParameter<?> p: existingReferenceParamsToKeep) { 
    +                existingToKeep.put(p.getConfigKey().getName(), p);
    +            }
    +        }
    +
    +        List<SpecParameter<?>> result = MutableList.<SpecParameter<?>>of();
    +        for (SpecParameter<?> p: newParams) {
    +            if (p instanceof SpecParameterForInheritance) {
    +                SpecParameter<?> existingP = existingToKeep.remove(p.getConfigKey().getName());
    +                if (existingP!=null) {
    +                    p = ((SpecParameterForInheritance<?>)p).resolveWithAncestor(existingP);
    +                } else {
    +                    // TODO find config keys on the type (not available as parameters)
    +                    /* we don't currently do this due to low priority; all it means if there is a config key in java,
    +                     * and a user wishes to expose it as a parameter, they have to redeclare everything;
    +                     * nothing from the config key in java will be inherited */
    +                    p = ((SpecParameterForInheritance<?>)p).resolveWithAncestor((ConfigKey<?>)null);
    +                }
    +                result.add(p);
    +            } else {
    +                existingToKeep.remove(p.getConfigKey().getName());
    +                result.add(p);
    +            }
    +        }
    +        result.addAll(existingToKeep.values());
    +        return result;
    +    }
    +
    +    /** instance of {@link SpecParameter} which includes information about what fields are explicitly set,
    +     * for use with a subsequent merge */
    +    @SuppressWarnings("serial")
    +    @Beta
    +    static class SpecParameterForInheritance<T> extends BasicSpecParameter<T> {
    --- End diff --
    
    What's the case of having this as a separate class vs updating `BasicSpecParameter`?
    Personal preference to sticking with just `BasicSpecParameter`  ( + `Maybe` for the fields) to avoid `instanceof` checks. For persistence compat - could use the `readObject` trick.


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