public interface ConfigMergeable
Config and
ConfigValue. Instances of Config and ConfigValue can
be combined into a single new instance using the
withFallback() method.
Do not implement this interface; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.
| Modifier and Type | Method and Description |
|---|---|
ConfigMergeable |
withFallback(ConfigMergeable other)
Returns a new value computed by merging this value with another, with
keys in this value "winning" over the other one.
|
withFallback(ConfigMergeable other)
This associative operation may be used to combine configurations from multiple sources (such as multiple configuration files).
The semantics of merging are described in the spec for HOCON. Merging typically occurs when either the same object is created twice in the same file, or two config files are both loaded. For example:
foo = { a: 42 }
foo = { b: 43 }
Here, the two objects are merged as if you had written:
foo = { a: 42, b: 43 }
Only ConfigObject and Config instances do anything in
this method (they need to merge the fallback keys into themselves). All
other values just return the original value, since they automatically
override any fallback. This means that objects do not merge "across"
non-objects; if you write
object.withFallback(nonObject).withFallback(otherObject),
then otherObject will simply be ignored. This is an
intentional part of how merging works, because non-objects such as
strings and integers replace (rather than merging with) any prior value:
foo = { a: 42 }
foo = 10
Here, the number 10 "wins" and the value of foo would be
simply 10. Again, for details see the spec.other - an object whose keys should be used as fallbacks, if the keys
are not present in this one