Implementing a Resolver

To create your own a resolver subclass ReferenceResolver and implement the method resolve.

Name your resolver using by annotating your class with the @Type(string). The name provided by this annotation will expose your resolver to the Gyro language as $(<name>). Resolvers can be namespaced, similar to how resources are namespaced by provider, by adding to the package with your resolver. Annotate the package declaration in with the @Namespace(<name>) annotation. With a namespace defined your resolver will be available as $(<namespace>::<type>).

Your resolver’s resolve method will be called whenever Gyro encounters a reference with the name of your resolver in it. Your resolver will be passed in a Scope object, this gives you access to Gyro’s internal scope (map of values), and a List<Object> of arguments that have already been resolved.

Your resolver should return a value that can be used by the Gyro configuration language. Typically this means returning a basic type (integer, string, list, or map) or a Resource.


The following example shows the implementation of a simple resolver called the string-concat that concatenates two or more stings.

public class StringConcatResolver extends ReferenceResolver {

    public Object resolve(Scope scope, List<Object> arguments) throws Exception {
        if (arguments.size() < 2) {
            throw GyroException("The 'String-concat' resolver needs at least two arguments");

        return String.join(" ", arguments);