Create a message

Sisyphus provides an easy-to-use DSL API for building Message instances in Kotlin using Protobuf.

message EchoResponse {
    string content = 1;

    Severity severity = 2;
}

The above proto file defines a Message named EchoResponse, and the next step is to create an EchoResponse instance directly using the EchoResponse DSL.

val response = EchoResponse {
    this.content = input.content
    this.severity = input.severity
}

A Message can be constructed by simply using curly brackets after the Message type, and properties can be freely set in the {} code block.

Can't find the EchoResponse type?

Try executing generateProtos in the Gradle Task window to generate all the Kotlin code.

Immutable and mutable types of messages

Sisyphus provides two access interfaces for all messages, for example, in the above example, Sisyphus generates two interfaces for EchoResponse messages. They are EchoResponse and MutableEchoResponse.

EchoResponse is an immutable interface and is the basic entry point for accessing Protobuf messages, in general we just need to import this interface.

MutableEchoResponse is a mutable interface, normally hidden by various message DSLs, and will be placed in a special internal package.

EchoResponse { // this: MutableEchoResponse
    this.content = input.content
    this.severity = input.severity
}

For example, in the above example, MutableEchoResponse access is provided in the code field expanded by the EchoResponse DSL.

Once a message is removed from the creation of a message DSL code field, it is immutable access. See Kotlin's var and val design for more information on the benefits of mutable and immutable access.

Reassigning values to messages

Once the message has been created, the MutableEchoResponse DSL domain can be re-expanded via the invoke DSL.

val response = EchoResponse {
    this.content = input.content
    this.severity = input.severity
}
val newResponse = response.invoke { // can also be omitted as `response {`
    this.content = "new content"
}

Attention

However, it is worth noting that the invoke DSL creates a new Message instance rather than assigning a value to the original instance.

response !== newResponse // response and newResponse are not the same object