What is 'dashed'?
It was a fine blue morning, growing soft after an early frost, and no day, as Williams had pointed out, to waste on the Bennys of this life; but the sight of Trimmings standing up unblushingly in the bright sunlight restored Grant's wavering good humour. Last night it had been a lighted doorway in the dark. Today it stood revealed, extravagantly monstrous, in all its smug detail, and Grant was so enraptured that his foot came down on the brake and he brought the car to a standstill at the curve of the drive, and sat there gazing.
'I know just how you are feeling,' a voice said at his elbow. And there was Liz; a little heavy-eyed, he noticed, but otherwise calm and friendly.
'Good morning,' he said. 'I was a little dashed this morning because I couldn't drop everything and go fishing. But I feel better now.' (Chapter 11 To Love and Be Wise)'It is a beauty, isn't it,' she agreed. 'You don't quite believe it is there at all. You feel that no one could possibly have thought it up; it just appeared.'
What does the last sentence mean?

Question

What is 'dashed'?
It was a fine blue morning, growing soft after an early frost, and no day, as Williams had pointed out, to waste on the Bennys of this life; but the sight of Trimmings standing up unblushingly in the bright sunlight restored Grant's wavering good humour. Last night it had been a lighted doorway in the dark. Today it stood revealed, extravagantly monstrous, in all its smug detail, and Grant was so enraptured that his foot came down on the brake and he brought the car to a standstill at the curve of the drive, and sat there gazing.
'I know just how you are feeling,' a voice said at his elbow. And there was Liz; a little heavy-eyed, he noticed, but otherwise calm and friendly.
'Good morning,' he said. 'I was a little dashed this morning because I couldn't drop everything and go fishing. But I feel better now.' (Chapter 11 To Love and Be Wise)'It is a beauty, isn't it,' she agreed. 'You don't quite believe it is there at all. You feel that no one could possibly have thought it up; it just appeared.'
What does the last sentence mean?

Answer

I agree with Basil and Eigo. It means 'down' or disappointed, not 'rushed'.

Answer

I agree with Basil, Eigo and Su.Ki.

Answer

In this case, 'dashed' does not mean 'rushed'. It means 'disappointed' or 'dispirited'.

Answer

Dashed is the same as Hurried, When You need to  Run or travel somewhere in a great hurry:

Examples:

I dashed into the garden.

I must dash, I’m late.

So, in Your text When You see the expression " Little dashed", means that the person was a worried to hurry for other place quickly.

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“虚线是一样的匆匆，当你需要运行或在急急忙忙旅游的地方：

例如：

我冲进花园。

我必须冲，我来晚了。

所以，在你的文字，当你看到表达式“小冲”，指的人是忧心忡忡，迅速赶紧其他地方。

Answer

In my opinion, this is a non-standard use of the verb "dash". The only meaning I can infer from the context is that "'I was a little dashed" ==  "I felt disappointed, unhappy, gloomy, sad, dispirited"; take your pick. Might be connected to the idiom "hopes being dashed" where "dashed" == "destroyed, broken to pieces". Another example of Tey's "creative" and mystifying use of the language, to be sure. The last sentence refers to the sight of "Trimmings", whatever that is (possibly a manor or castle of some sort?). The building seems to be very beautiful, almost magical in its appearance, at least to the speaker and Grant.