That RFC does not define anything about these so-called "matrix" path parameters. It merely states that you may use those characters to delimit sub-segments inside of a single path segment. The link you supply which states the RFC defines anything about path parameters is inaccurate.

However, this can already be accomplished by using your own annotation, a Map type, and a registered string converter which renders the object to a String using whatever mechanism and joining characters that you want.

Since it's not part of any official HTTP spec and you can build this into Retrofit using its existing extension mechanisms, I'm inclined not to do anything here.

I would welcome this as a sample, in fact.

That RFC does not define anything about these so-called "matrix" path parameters. It merely states that you may use those characters to delimit sub-segments inside of a single path segment. The link you supply which states the RFC defines anything about path parameters is inaccurate.

However, this can already be accomplished by using your own annotation, a Map type, and a registered string converter which renders the object to a String using whatever mechanism and joining characters that you want.

Since it's not part of any official HTTP spec and you can build this into Retrofit using its existing extension mechanisms, I'm inclined not to do anything here.

Can you provide link to reference documentation which describe how to do it with custom annotation, map and a registered string converter. Or some similar case.

The javadoc for @Path talks about how values are encoded by asking the Retrofit.stringConverter() method. The Type and an array of parameter Annotation instances are supplied to that method which are forwarded to every registered Converter.Factory's stringConverter method. From that method, if you can handle the type, you return a Converter that takes the object and converters it to a string however you choose.

We have a sample which uses a JSON serializer to convert a query param using this mechanism: https://github.com/square/retrofit/blob/00e82dfbe19fd1a9b725b134b70dafe6a0bde8f4/samples/src/main/java/com/example/retrofit/JsonQueryParameters.java