Task never completes

[dimazen]

When your framework compiled with optimizations (try to install via Carthage) assert is not checked. Therefore this code from the TaskCompletionSource is never executed:

    public func setResult(result: TResult) {
        assert(task.trySetState(.Success(result)), "Can not set the result on a completed task.")
    }

As Apple mentions:

/// Traditional C-style assert with an optional message.
....
/// * In -O builds (the default for Xcode's Release configuration),
///   `condition` is not evaluated, and there are no effects.

[nlutsenko]

(－‸ლ) You are absolutely correct, we should indeed use a precondition here, so it's not optimized away.

[dimazen]

I would suggest to distinguish execution and evaluation, since precondition can be ignored under some settings:

/// * In -Ounchecked builds, `condition` is not evaluated, but the
///   optimizer may assume that it *would* evaluate to `true`. Failure
///   to satisfy that assumption in -Ounchecked builds is a serious
///   programming error.