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From geomacy <...@git.apache.org>
Subject [GitHub] brooklyn-server pull request #462: Inherit config default values
Date Tue, 03 Jan 2017 17:04:37 GMT
Github user geomacy commented on a diff in the pull request:

    https://github.com/apache/brooklyn-server/pull/462#discussion_r94415792
  
    --- Diff: core/src/main/java/org/apache/brooklyn/core/config/BasicConfigInheritance.java
---
    @@ -28,51 +32,188 @@
     import org.apache.brooklyn.config.ConfigKey;
     import org.apache.brooklyn.config.ConfigValueAtContainer;
     import org.apache.brooklyn.util.collections.CollectionMerger;
    +import org.apache.brooklyn.util.exceptions.Exceptions;
     import org.apache.brooklyn.util.exceptions.ReferenceWithError;
     import org.apache.brooklyn.util.guava.Maybe;
    +import org.apache.brooklyn.util.text.Strings;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
     
    +@SuppressWarnings("serial")
     public class BasicConfigInheritance implements ConfigInheritance {
     
    +    private static final Logger log = LoggerFactory.getLogger(BasicConfigInheritance.class);
    +    
         private static final long serialVersionUID = -5916548049057961051L;
     
         public static final String CONFLICT_RESOLUTION_STRATEGY_DEEP_MERGE = "deep_merge";
         public static final String CONFLICT_RESOLUTION_STRATEGY_OVERWRITE = "overwrite";
         
    +    public static abstract class DelegatingConfigInheritance implements ConfigInheritance
{
    +        protected abstract ConfigInheritance getDelegate();
    +        
    +        @Override @Deprecated public InheritanceMode isInherited(ConfigKey<?> key,
Object from, Object to) {
    +            return getDelegate().isInherited(key, from, to);
    +        }
    +        @Override public <TContainer, TValue> boolean isReinheritable(ConfigValueAtContainer<TContainer,
TValue> parent, ConfigInheritanceContext context) {
    +            return getDelegate().isReinheritable(parent, context);
    +        }
    +        @Override public <TContainer, TValue> boolean considerParent(ConfigValueAtContainer<TContainer,
TValue> local, ConfigValueAtContainer<TContainer, TValue> parent, ConfigInheritanceContext
context) {
    +            return getDelegate().considerParent(local, parent, context);
    +        }
    +        @Override
    +        public <TContainer, TValue> ReferenceWithError<ConfigValueAtContainer<TContainer,
TValue>> resolveWithParent(ConfigValueAtContainer<TContainer, TValue> local, ConfigValueAtContainer<TContainer,
TValue> resolvedParent, ConfigInheritanceContext context) {
    +            return getDelegate().resolveWithParent(local, resolvedParent, context);
    +        }
    +        @Override
    +        public boolean equals(Object obj) {
    +            return super.equals(obj) || getDelegate().equals(obj);
    +        }
    +        
    +        // standard deserialization method
    +        protected ConfigInheritance readResolve() {
    +            return returnEquivalentConstant(this);
    +        }
    +    }
    +
    +    private static ConfigInheritance returnEquivalentConstant(ConfigInheritance candidate)
{
    +        for (ConfigInheritance knownMode: Arrays.asList(
    +                NOT_REINHERITED, NOT_REINHERITED_ELSE_DEEP_MERGE, NEVER_INHERITED, OVERWRITE,
BasicConfigInheritance.DEEP_MERGE)) {
    +            if (candidate.equals(knownMode)) return knownMode;
    +        }
    +        if (candidate.equals(new BasicConfigInheritance(false, CONFLICT_RESOLUTION_STRATEGY_OVERWRITE,
true, true))) {
    +            // ignore the ancestor flag for this mode
    +            return NEVER_INHERITED;
    +        }
    +        return candidate;
    +    }
    +    
    +    /*
    +     * use of delegate is so that stateless classes can be defined to make the serialization
nice,
    +     * both the name and hiding the implementation detail (also making it easier for
that detail to change);
    +     * with aliased type names the field names here could even be aliases for the type
names.
    +     * (we could alternatively have an "alias-for-final-instance" mode in serialization,
    +     * to optimize where we know that a java instance is final.)   
    +     */
    +    
    +    private static class NotReinherited extends DelegatingConfigInheritance {
    +        final static BasicConfigInheritance DELEGATE = new BasicConfigInheritance(false,
CONFLICT_RESOLUTION_STRATEGY_OVERWRITE, false, true); 
    +        @Override protected ConfigInheritance getDelegate() { return DELEGATE; }
    +    }
         /** Indicates that a config key value should not be passed down from a container
where it is defined.
          * Unlike {@link #NEVER_INHERITED} these values can be passed down if set as anonymous
keys at a container
          * (ie the container does not expect it) to a container which does expect it, but
it will not be passed down further. 
          * If the inheritor also defines a value the parent's value is ignored irrespective

          * (as in {@link #OVERWRITE}; see {@link #NOT_REINHERITED_ELSE_DEEP_MERGE} if merging
is desired). */
    -    public static BasicConfigInheritance NOT_REINHERITED = new BasicConfigInheritance(false,CONFLICT_RESOLUTION_STRATEGY_OVERWRITE,false);
    +    public static ConfigInheritance NOT_REINHERITED = new NotReinherited();
    +    
    +    private static class NotReinheritedElseDeepMerge extends DelegatingConfigInheritance
{
    +        final static BasicConfigInheritance DELEGATE = new BasicConfigInheritance(false,
CONFLICT_RESOLUTION_STRATEGY_DEEP_MERGE, false, true); 
    +        @Override protected ConfigInheritance getDelegate() { return DELEGATE; }
    +    }
         /** As {@link #NOT_REINHERITED} but in cases where a value is inherited because a
parent did not recognize it,
          * if the inheritor also defines a value the two values should be merged. */
    -    public static BasicConfigInheritance NOT_REINHERITED_ELSE_DEEP_MERGE = new BasicConfigInheritance(false,CONFLICT_RESOLUTION_STRATEGY_DEEP_MERGE,false);
    -    /** Indicates that a key's value should never be inherited, even if defined on a
container that does not know the key.
    -     * Most usages will prefer {@link #NOT_REINHERITED}. */
    -    public static BasicConfigInheritance NEVER_INHERITED = new BasicConfigInheritance(false,CONFLICT_RESOLUTION_STRATEGY_OVERWRITE,true);
    +    public static ConfigInheritance NOT_REINHERITED_ELSE_DEEP_MERGE = new NotReinheritedElseDeepMerge();
    +    
    +    private static class NeverInherited extends DelegatingConfigInheritance {
    +        final static BasicConfigInheritance DELEGATE = new BasicConfigInheritance(false,
CONFLICT_RESOLUTION_STRATEGY_OVERWRITE, true, false);
    +        @Override protected ConfigInheritance getDelegate() { return DELEGATE; }
    +    }
    +    /** Indicates that a key's value should never be inherited, even if inherited from
a value set on a container that does not know the key.
    +     * (Most usages will prefer {@link #NOT_REINHERITED}.) */
    +    public static ConfigInheritance NEVER_INHERITED = new NeverInherited();
    +    
    +    private static class Overwrite extends DelegatingConfigInheritance {
    +        final static BasicConfigInheritance DELEGATE = new BasicConfigInheritance(true,
CONFLICT_RESOLUTION_STRATEGY_OVERWRITE, false, true);
    +        @Override protected ConfigInheritance getDelegate() { return DELEGATE; }
    +    }
         /** Indicates that if a key has a value at both an ancestor and a descendant, the
descendant and his descendants
          * will prefer the value at the descendant. */
    -    public static BasicConfigInheritance OVERWRITE = new BasicConfigInheritance(true,CONFLICT_RESOLUTION_STRATEGY_OVERWRITE,false);
    +    public static ConfigInheritance OVERWRITE = new Overwrite();
    +    
    +    private static class DeepMerge extends DelegatingConfigInheritance {
    +        final static BasicConfigInheritance DELEGATE = new BasicConfigInheritance(true,
CONFLICT_RESOLUTION_STRATEGY_DEEP_MERGE, false, true);
    +        @Override protected ConfigInheritance getDelegate() { return DELEGATE; }
    +    }
         /** Indicates that if a key has a value at both an ancestor and a descendant, the
descendant and his descendants
    -     * should attempt to merge the values. If the values are not mergable behaviour is
undefined
    +     * should attempt to merge the values. If the values are not mergeable behaviour
is undefined
    --- End diff --
    
    I know the "behaviour is undefined" wasn't introduced in this PR, but reading it now makes
me question whether this is a desirable state of affairs, or whether this introduces a potential
source of confusing and inconsistent behaviours of different implementations.  Could we use
this PR as an opportunity to replace this "behaviour is undefined" with a clearer behaviour
- either overwrite, or maybe throw a well known exception in order to highlight the merge
problem?


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