How is the result returned in SharpDX.DirectInput.Device.Acquire()?

I believe the correct way to use the Acquire method is to assume it has worked correctly - if it fails to acquire the device, a SharpDXException will be thrown from the Acquire method. In this way, there is no need for a return value.

A disassembly of the Acquire method shows the code as:

public unsafe void Acquire()
{
  // ISSUE: cast to a function pointer type
  // ISSUE: function pointer call
  (Result) (__calli((__FnPtr<int (void*)>) *(IntPtr*) (*(IntPtr*) this._nativePointer + IntPtr(7) * sizeof (void*)))(this._nativePointer)).CheckError();
}

The CheckError call is a method on the Result struct, which looks like this:

/// <summary>
/// Checks the error.
/// </summary>
public void CheckError()
{
    if (_code < 0)
    {
        throw new SharpDXException(this);
    }
}

(Source from https://github.com/sharpdx/SharpDX/blob/b1596ddd38a5de77704412910a4fb265a4ab8525/Source/SharpDX/Result.cs)

I suppose you could invoke GetLastError(). but depending on how your program is structured it might contain a stale value (for example, if an earlier call failed and Acquire() succeeded but did not clear the error code) and it might not be accurate depending on how that SharpDX function is written.

You could work around the "stale" issue by invoking SetLastError() to prime (clear) the error code before invoking SharpDX.