setup.md

eDO Setup Guide

How to build your project with eDO

If you are using Bazel, normally, you will have at least two BUILD files

BUILD for the Host and YourClass

# The Host binary that starts the EDOHostService.
objc_library(
    name = "Host",
    srcs = [
      "Host.m",
    ],
    deps = [
      ":YourClass",  # Your actual class implementation
      "//third_party/objective_c/eDistantObject",
    ]
)

# YourClass library
objc_library(
    name = "YourClass",
    srcs = ["YourClass.m"],
    deps = [":Headers"],
)

# Expose YourClass headers as a separate target so the client can use it
# without linking the binary.
objc_library(
    name = "Headers",
    hdrs = ["YourClass.h"],
    # If there is any deps, make sure it will not introduce any binary unit that
    # is going to link with the client.
)

BUILD for the Client to use YourClass

# The client that uses YourClass from a different process.
objc_library(
    name = "Client",
    srcs = ["Client.m"],
    deps = [
        ":Headers",
        "//third_party/objective_c/eDistantObject",
    ]
)

This is an example using Bazel. For other build tools, the rule is to import headers and implementations in one process, while import only headers in the other process who makes remote invocations using methods defined in the headers.

Where to write code

When you need to write code that will jump between two processes, it can be confusing to say in which process the actual implementation and its stub/proxy call should be.

For example, you already have an API in the host process to get the element from an internal array, and you need another API to do some complicated logic to process the number in client process. In this case, since only the host process has access to the internal data, we should keep the old API in host process and let the client process hold a distant object of it.

// In the host process

@implementation HostDistantObject {
  NSArray<NSNumber *>* _myArray;
}

- (NSNumber *)getNumber:(NSInteger *)index {
  return [_myArray objectAtIndex:index];
}

@end

// In the client process
- (void)processFirstNumber {
    NSNumber *firstNumber = [HostDistantObject.sharedInstance getNumber:0];
    // Do some complicated logic with the remote object firstNumber...
}

In the example above, the client process holds a remote instance of HostDistantObject. And the API getNumber: actually runs in host process. Then the client process receives another remote instance of NSNumber and can do whatever logic on it.