waitForEx

waitForEx

DCli goes to great lengths to remove the need to use Futures and await;there are two key tools we use for this.

waitFor and streams.

waitFor is a fairly new Dart function which ONLY works for Dart CLI applications and can be found in the dart:cli package.

The DCli API doesn't expose any futures despite using futures extensively in its internal workings.

waitFor allows a Dart CLI application to turn what would normally be an async method (returning a future) into a normal synchronous method by effectively 'absorbing' a future. Normally in Dart, as soon as you have one async function, its async all of the way up.

DCli simply wouldn't have been possible without waitFor.

waitFor does however have a problem. If an exception gets thrown whilst in a waitFor call, then the stacktrace generated will be a microtask based stack trace. These stacktraces are useless as they don't show you where the original call came from.

This is why waitForEx was born. waitForEx is my own little creation that does three things.

1. capture the current stack using StackTraceImpl

2. calls waitFor and catches any exceptions

3. If an exception is thrown it patches the stack trace captured in 1 and merges it with the interesting bits of the microtask exception.

The result is that you get a clean stacktrace that points to the exact line that cause the problem and we have a stacktrace that actually shows where it was called from.