Promise

Promises/Deferred/Futures for C++

How to develop:

Natively on your computer

1. Install clang++-3.7 (Ensure it can be run as clang++-3.7)
2. run make test

Installing clang++-3.7 is a bit non-trivial. On an Ubuntu machine, if you are lucky, you might be able to just run image/load.sh. This is provided without support, and is more just an approximate documentation of how I set up my build environment.

See image/Dockerfile for another way to set up the environment on Ubuntu 16.04.

Using docker

1. run cp local.mak.docker local.mak
2. run make test

This sets an environment variable in the Makefile that will use ./run.sh to run all actual build commands. ./run.sh is a small bash script that runs build commands in a docker container. The docker container has a full clang 3.7 build environment. The docker container is built from image/makeimage.sh and image/Dockerfile.

Design Thoughts:

Let T denote a type that is either movable or copyable.

Let Result<R, F> represent a value that has either type R or F.

A promise is constructed with:

• a set of Ts (S) that it can be resolved to.
• a set of Ts (F) that it can be rejected to.

The promise needs to provide 3 interfaces.

• a "callable" that can be called with any of S.
• a "callable" that can be called with any of F.
• an ChainLink<S, F> that has the following methods:
  • Then - takes a callable that can receive any of S and returns R or Result<R, Fr>.
    • Returns ChainLink<R, F+Fr>
  • Catch - takes a callable that can receive any of F and returns R or Result<R, Fr>
    • Returns ChainLink<S+R, Fr>
  • ThenCatch - takes two callables as above that must return the same R and Fr
    • Returns ChainLink<R, Fr>