Returns a new value computed by merging this value with another, with keys in this value "winning" over the other one.
Returns a new value computed by merging this value with another, with keys in this value "winning" over the other one.
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.
an object whose keys should be used as fallbacks, if the keys are not present in this one
a new object (or the original one, if the fallback doesn't get used)
Marker for types whose instances can be merged, that is Config and ConfigValue. Instances of
Config
andConfigValue
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.